Generally, an undergraduate CV will have a handful of major headings (education plus other sections as applicable such as publications, presentations, awards, research experience, clinical experience, professional societies). Not all of these headings will apply to you. For instance, if you don't have any publications then you'll omit that heading. Your CV might not exceed 1-2 pages, and that's to be expected at the undergraduate stage.
The research and clinical experience sections are tricky because you often won't see these sections on a faculty CV. But if you're just starting out in your career these sections are still helpful. For each entry you should give the name and location of the setting, the PI/supervisor's name, and a few bullet points with major responsibilities or accomplishments. This should take up no more than 4-5 lines in total for each entry. Use good judgment. If you worked in a lab for two continuous years and had important responsibilities there, that merits a higher level of detail/elaboration than spending a couple of months in a summer research program.
In the end, the specific format is not as important as the content. Whatever format/structure you choose, be consistent. Look at faculty and grad students' CVs for examples when possible. Make it neat, readable, and reflective of your actual career development stage. Resist to urge to pad your CV with things that don't really belong there, and don't embellish or make accomplishments out to be more than they are.
