Is apple TV able to just mirror my IMac and show exactly what I’m doing EG word processing or does it just work through apps like Chromecast?

It can mirror. Not sure how you do it on a Mac, my Macbook is too old to have airplay, but on an iPad/iPhone there is a switch in the airplay menu to mirror, so assume it will be the same with a Mac.

Yes it can you can mirror or extend desktop

It will mirror IF you have one new enough to allow Airplay.
If not there is an app you can download that will do it – can’t remember the name of it right now but just do a search.

Perfect thanks guys!

If you’re hoping to stream video fro your mac it will be very notchy and not at all smooth.
You can’t also connect a dvd drive and stream movies to your tv.
Considering its an apple product streaming stuff to an apple product, it’s not very good imo. Hopefully, the new one will be better.

Would I be better off just hardwiring a HDMI cable? I’d prefer AppleTV as I have a Iphone and Ipad too so can stream from them all. DVD isn’t an issue it’s just for streaming online and Iplayer really

There is an app called idisplay which will work on non airplay macs to mirror the screen.

I disagree iolo – used it loads to stream stuff from Putlocker, etc to the TV.
Thats with the Mac downstairs in the office and the ATV upstairs in the living room.
If you’re having issues you might want to check your wifi network first.