I sliced the top of my finger today and urgent fixed it for methey tested my movement too. i started typing without that finger now my forearm aches?

It'll be sore: You probably don't want to do too much with that hand until the pain dies down. Should take 2-3 days. If you keep using it, it probably won't injure you, but you sure will be sore. The more pain you have, the further it travels.

U strained the : Muscles in ur forearm by the altered mechanics of typing without the injured finger.More work and strain of the other 3 fingers which are moved by the muscles in the forearm.