What exactly is "grad school?" 

"Grad school" in psychology refers to graduate programs where students can pursue specialized education and advanced degrees in psychology, typically with the goal of becoming an academic (i.e., a professor) or a clinician (a clinical psychologist). We call students in these programs "grad students;" students who are still completing their BA or BSc are called "undergrads." 

Undergrads usually apply to grad school in their 4th (or final) year of their undergraduate studies; these applications are due in the late fall/early winter for entrance in the following year. Grad students in psychology typically complete a Master's degree and then a PhD ("doctoral degree"); these programs don't typically recruit students who only wish to complete a Master's degree, as a PhD is the necessary degree for an academic career or a career as a clinical psychologist. 

Graduate school in psychology is grouped into two main categories: Experimental psychology and clinical psychology. These programs are offered by psychology departments. 

Experimental psychology 

This type of program trains students to be researchers, creating new knowledge through their work. Students in these programs typically have the goal of becoming an academic (professor!). Increasingly, graduates of these programs are finding new and unique ways to apply their skills and talents in a variety of employment areas, including business, industry and government. 

Experimental programs encompass areas like social, developmental, cognitive neuroscience, behavioral neuroscience, cognition, sensation & perception, animal cognition, personality, measurement/quantitative, industrial/organizational, forensic, and health psychology. (Areas like industrial/organizational, health, and forensic are only offered at some universities; 

Canadian universities use a mentorship model in their graduate training. This means that the grad student works closely with one professor who trains and supervises the student's research. Doctoral programs in experimental psychology typically have only limited coursework, as most of the grad student's time is devoted to developing their research skills. 

Clinical psychology 

Most clinical PhD programs in Canada follow scientist-practitioner approach: Students are trained both as researchers and clinicians, informed by evidence-based practice (i.e. using research to provide the best treatment for patients). 

A PhD in clinical psychology usually leads to a career as a clinical psychologist (i.e., a clinician who works in hospitals, private practice, schools, prisons, etc.), professor, or researcher. 

Students usually specialize their training, to focus on adults, children, or neuropsychology.  

Similar to experimental programs, most schools use a mentorship model, where students work closely with one professor who trains and supervises the student's research.  

Clinical students typically have a heavier course load in their early years in graduate school, to serve as a foundation for their clinical training. 

It's a great idea to have gained some experience volunteering in a helping field before applying to clinical psychology to (a) ensure you enjoy this kind of work, and (b) to improve the quality of your application. 

Some US schools offer a PsyD in clinical psychology; as I understand, the PsyD degree places relatively little emphasis on scientific research compared to a PhD program (see this article). But in Canada, a doctoral degree in psychology is called a PhD.

Following completion of the Ph.D., trainees complete a 1-year residency (typically in a hospital) and then write board certification exams. Trainees who are successful then complete 1-year of supervised practice.

Some schools offer other specialized areas in psychology: Forensic psychology and community psychology are offered at a handful of schools in Canada

Forensic psychology 

Forensic psychology (also: Law-Forensic, or Psychology-Law) programs may be based in experimental psychology or clinical psychology.

In Canada, specialized programs in forensic psychology are at three universities: Carleton UniversitySimon Fraser University, and the University of Ontario Institute of Technology (UOIT)

There are also individual academics who do research in forensic psychology at many other schools, including King's at Western (me!), Wilfrid Laurier, UBC Okanagan, Ryerson, Memorial, Windsor, Saskatchewan, Thompson Rivers, Brock, OISE (U of T), and others.

Forensic clinical psychologists focus their clinical practice on offender populations. At last check, Correctional Service Canada was the country's largest employer of forensic psychologists, with some 300 on the payroll.

Forensic experimental psychologists conduct research that addresses applied questions at the intersection of psychology and law; this includes things like eyewitness memory, jury decision-making, and investigative interviewing.

Community psychology 

This is a unique MA program, offered at Wilfrid Laurier Univeristy. Their MA in Community Psychology program includes "a practicum (field work) placement in a community, organizational, and/or government setting." 

Uh, how long will I be in school?!

All told, grad school, from Master's to PhD is usually about 6-8 years. 

It typically takes 2 years to complete a Master's degree, and 4 years to complete a PhD degree. 

Clinical students also complete a 1-year residency (typically in a hospital) after they finish their PhD; then, they write board certification exams and those who are successful complete 1-year of supervised practice. 

Students who wish to pursue an academic position (i.e., be a professor) almost always complete a post-doc; this is typically a 2 to 3 year trainee position in a lab where the recently-minted PhD further develops their academic research program with more autonomy than a graduate student. 

Note, however, that graduate school isn't a whole lot like undergrad; it's really like the first step in your professional career, and feel much more like a job, with normal 9-5-type working hours in the lab. Grad students in psychology are typically well-funded during their studies; they receive funding packages in the form of a combination of scholarships (tax-free income!) and/or teaching-assistantships. This means that grad students in psychology don't typically incur loans and debt or need to work part-time jobs. 

It's worth pointing out that most graduate programs in psychology primarily accept students who plan to complete their doctoral degree, since the doctoral degree is typically required for a research career (e.g., a professor, research scientist) or to be licensed as a clinical psychologist (except in Quebec).