[UK] Complete noob looking for very cheap first setup

Hi, im looking to upgrade over some rubbish computer speakers for my room and read that some bookshelf speakers is the best way to do that. I've found on gumtree some Eltax's for £25, which appears to be a good deal (although i have no experience with what is or not). What kind of amp would i need to look for to drive them? I don't really understand the relationship between watts of the speakers and amp. I'm effectively trying to do as cheap as reasonably possible.

Thanks