.......So if I mining how do I get the transaction fee for other transactions.
You'll probably be pooled mining, so if as a miner you want your share of the transaction fee, mine at a pool that also pays the trandaction fee to miners. Not all pools do that yet.
..... also if we have coins already surely if we send them to someone else they should go to directy to them as we use p2p.
Is this not the case?
The coins don't go anywhere. Instead, imagine a huge ledger that everyone shares. If you send coins to someone else, a debit is written in the ledger for you, and a credit for whomever wished to credit the coins.
You might need to read
the wiki for a bit - lots of good answers there.