The first thing to do is look through the Undergraduate Handbook [current] and check through the requirements for your degree(s), keeping in mind that you may, at your option, use the handbook from the year you started going to the school, instead of the current one. After reviewing the requirements, look through the General Bulletin [current] for your department. In many cases, there is even a nice little roadmap (of courses) that you can use to help plan what courses you will take (which is important because many classes are only offered in the Fall or Spring semester).

The General Bulletin is suffused with descriptions of the different departments, and the faculty, laboratories, and classes therein. Browsing through the class list, you may look at these descriptions and perhaps find tech electives. To find out if a class is offered during a certain semester, who teaches it, and in which time slot it falls, you may search at the Searchable Schedule of Classes and simultaneously look at the ratings for the teacher (occasionally listed incorrectly in the schedule) at ratemyprofessor.com. Write down the CRN numbers for the courses you want to take, because you will want them when registering.

Once you've found some classes you want to take, you need to login to SOLAR to register for them. This is a non-trivial operation. Using SOLAR requires the Opal Player Plugin and a sufficient quantity of grim determination, a remote desktop client (see SOLAR), or a 15-minute walk to the Nord Computer Lab (open all the time if you have a Case ID). The terminals in the new dorms also have SOLAR installed.

Hilariously, SOLAR has hours:

The hours are Monday through Thursday 7:00 a.m. - 8:00 p.m., Friday 7:00 a.m. - 7:00 p.m. and Saturday 9:00 a.m. - 7:00 p.m.

The university has decided that you must obtain a special PIN number from your academic advisor (available on the my case portal in the middle, if you don't know who it is, though you'll have to look up their name in the phone book) in order to register. You should do this as soon as possible simply because it's really handy to be able to change your classes when you want (provided SOLAR is up, it actually has hours of operation). Upper classmen will be interested in registering as early as possible because they are given a two-dayish window before the class below them may register. For freshmen really intent on registering for classes early, SOLAR used to go down on the registration day, and you'd have to get in line in Yost to register with paper. Since then, SOLAR has upgraded to substantially more connections and it may not go down as much.

It may also be nice to look at the Academic Calendar in order to see the dates you may add and/or drop classes, though the last day to withdraw (or pass/fail) much be listed some place else. For the confused, there is always the official guide and the FAQ.