Very confusing and can't make images expand

Hi folks, I’m new to WordPress and so far I’m not having a great time with it.

All I want to do was set up a simple little blog that I can write in now and again but I’m finding WordPress extremely fiddly and confusing but there seems to be a lack of basic features with the theme I’m using.

In particular the only feature I really need is that I want my readers to be able to click on an image in the post which enlarges it but I can not for the life of me see a way to do this. This is all I want really and my account doesn’t seem to have any of the options that some of the online tutorials have.

Other tutorial say that I need to edit the CSS to get these effects and It’s something that I just can’t be bothered with for a project that’s this small and meant to be quick and fun.

I’m also confused as there seems to be a downloadable version of WordPress whereas I just signed up online and picked a theme.

Any help would be appreciated.

Thank you!