Here is an excellent resource that will answer most of your questions. In my boiled down style, here you go:
1. Assume your child will go to college.
2. Find out what high school courses colleges in your state require for admission. Just do an internet search for a nearby college and check their admissions pages.
3. On a practice transcript copy, write out those courses over the four years. If a college says they want four years of English, call your high school courses English I, English II, English III and English IV.
4. Every year, make sure your student is doing things and reading material that correspond to those required courses. Keep notes and a file folder full of proof.
5. Your child will be doing much more than the required courses, and those will be "electives" or extra courses that every high school offers. To get ideas for what to call those courses, check out public high school websites. They often have a course catalog online. Here's an example from a small town near us. Giving public school names to your homeschooling classes makes things easier on your admissions officer.
6. Give normal A, B, C grades. See the resource I linked to at the beginning for a very helpful explanation of grading and assigning credit.
7. Keep each semester to six or seven classes. That's the normal load. Our local public school has seven class periods, and a student can take study hall, so that's really six classes.
8. Any learning or time spent on useful things that goes beyond the six or seven transcript-able classes should be listed as extra curricular activities. It's amazing how long this can be. Think through any volunteer work, pay job, music classes, sports, clubs, obsessions...
9. And don't forget to take the ACT and/or the SAT. You can take them as many times as you want, beginning at any age. Every SAT score will be sent to colleges, but you get to pick which ACT score to send, so keep that in mind. Also, some schools will limit how long a score is valid. In other words, they probably won't accept a score your child got five years ago. Here's the ACT site, and here's the SAT site. You can pick your testing location, sign up, and pay online.
That's all I can think of right now! Homeschooling high school can be a lot of fun, giving your child a chance to explore and mature without all the high school drama. :)
My transcript blank is here.