Steps
1. Do not contact the cat. You may just damage it even more.
2. Contact creature preserve.
3. Tell an mature. If you are under 16 you should probably tell an mature.
4. If its accidents aren't too bad, get it in a card board box with a cover and air gaps and take it to the regional creature haven.
Tips
Give it some meals and a consume of normal water, but not dairy - unless it is professional cat dairy, regular dairy angers pet's bellies.
Warnings
Be very cautious of being attacked or scraped by any cat.
If the cat is in the street, and you want to just keep it, at least put it on the footpath.
Be cautious, as it may have ticks.