Most likely yes. Ph.D. programs are typically research-oriented and competitive applicants should be well-prepared to engage in both the coursework and research expectations associated with the program. One of the best ways to prepare is by engaging in research as an undergraduate student.
This depends on the nature of the research lab and the project you'll be working on. As you start out in a lab, you might be responsible for tasks such as data entry and collection, running experiments, and administering surveys. As you learn and spend more time in the lab, your responsibilities might increase. You might be able to help out with the literature review for a project, contribute to a scientific poster, present at a conference, and design and run your own research study, culminating in an honors thesis.
This depends on the particular lab and the nature of the project you are working on. Your time committment could be as little as 3-4 hours per week or as many as 20 hours per week. As you apply for research positions make sure you are aware of the expected time committment and make sure you can balance it with your classes and other activities.
Typically yes. In some cases research labs may require that you be a student, particularly if the research position is funded. However, the vast majority of research labs allow individuals to volunteer regardless of whether they are currently a student. If you were unable to gain research experience while in school, you can always reach to a lab or faculty member to ask if they will consider you as a volunteer research assistant.