Need to ask you a number of questions before we can offer assistance:
1. What exact Mac model do you have?
2. What exact Mac OS do you have?
3. What Mac OS were you using previously, and how did you upgrade to the newer OS? Did you just upgrade "in place", ie, basically let the new OS over write the old one?
4. Have you ever done any disk cleanup/maintenance/repairs, from a software perspective? You can actually do quite a lot of disk cleanup on your own, and there are some excellent products available (both free and commercial) that can help you with that.
5. Are you making backups to an external device? That task is so, so critical. If you are doing that, what software do you use for that task?
6. How much space is on your internal drive?
7. Can you use another browser?
8. Did you try a search for Safari? The Mac OS includes Spotlight for searches, although I use (and prefer) the excellent free program EasyFind.
Once you let us know all that, we can help you better.