My tumbling composter...

[rabbit]

I haven't put anything in it since last october, not turned it
The stuff I put in last year hasnt really rotted down but I'm going to start putting my scraps in again now it's getting warmer

There's a stable nearby giving away bags of manure, can I put in in the tumbler too?

EDIT to add I inherited this compster and have not done composting before..

[Two_Sheds]

You need to check that the manure is aminopyralid-free, or else you will poison all your veggies.

You could put manure in a tumbler, but really it should be filling up on your kitchen scraps, weeds, waste paper, cardboard etc. Put the manure in a separate, covered heap.

[Two_Sheds]

haven't put anything in it since last october

Why? Aren't you eating anything?
You should be putting in EVERYTHING that's compostable: pet bedding, hoover contents, kitchen scraps, torn up paper, shredded newspaper, cardboard boxes, egg boxes, non-perennial weeds, dead plants etc

Grass clippings in one inch layers

and if you can bear to: urine. Yes, yours.

The stuff I put in last year hasnt really rotted down

It doesn't tend to do much over winter, action will start again when it warms up a bit in the spring.