This is a diagram showing how a scientific career generally progresses.
High/Middle School: Students can look for research opportunities in a local university, a summer program, school science research program etc. If you are interested in doing research, when choosing a university, you should consider whether or not the university has research opportunities. A small school (for example a small liberal arts school without a graduate school) might not have any active research for undergraduates to participate in whereas a larger school with a significant research focus will usually have a graduate program with research projects and a significant amount of resources undergraduates can take advantage of. Some schools that don’t have graduate schools might have less research projects, but they can have a larger percentage of their projects run by undergraduates.
University: In college, undergraduate students can start working in a lab to get experience, try out different fields, and start determining what they would like to study if they don’t know already. You can start as early as freshman year and by the end of your degree, you will most likely be able to do a senior thesis and run a project of your own. If you are depending on going on to do research in graduate school, this is highly recommended.
Graduate School (Masters): These are normally two year programs, which can have a research component where you complete a project and thesis at the end of the degree. More often these projects are suggested by an advisor since there isn’t enough time for a student to develop their own project. There is less individual funding available for these positions and many programs are phasing them out and only offering Ph.D. programs. Masters programs can be a great way to figure out what specific kind of research you want to work on and what you want any further research to focus on.
Graduate School (Ph.D.): You should get a Ph.D. if you want to direct the kind of research questions you answer. During your doctoral program, you can learn how to lead a larger project and how to ask scientific questions. Students enter programs both knowing and not knowing specifically what their project will be. You can either mostly work on a project your professor is interested in answering or come up with your own questions depending on how your lab and advisor function. Finding an advisor who you work well with and have the same interests as is a very important part of choosing a Ph.D. program.
Post doctoral studies: More people are doing a post doctoral study, or a post doc as their called. After getting your Ph.D., this is an opportunity to do another research project having some expertise and practice running a large project (your Ph.D. thesis). It’s usually from 1-3 years and sometimes scientists will do two postdocs before getting a more permanent position.
Professions: Academia, industry, and government are three general categories where there can be many positions for a scientist.