I know a lot about computers and stuff like that, so I could probably help a lot of people on sites such as superuser, but I also love to do coding, but I am still a total beginner, and so I ask a lot of questions on stackoverflow. If I earn any rep on either of the two sites, will that rep carry over to the other?
There's an association bonus that you can earn - if you earn 200 reputation on one site, then any other site you associate with it will earn a one-time bonus of 100 reputation. This is basically used for jumpstarting new accounts when you create them on new sites - it gives you the basic abilities of upvoting and commenting. It is an indirectly retroactive bonus - you can get it on sites you had previously associated prior to hitting 200, but you'll have to dissociate and then re-associate the accounts to get the bonus 100.
Past that, there is no carry-over. Different sites have different policies on various aspects, such as proper tagging or editing. So while you might have high experience with retagging and such on one site, this doesn't necessarily mean you have it with other sites. You need to build up familiarity with that site's policies in order to re-earn those privileges.