now say I have 5 bitcoins in one address. But if I make a transaction of 1 bitcoin, why does the remaining balance of 4 move to another address.
Because the change is being sent to a change address (it's for your own "privacy").
Is there a way for it to stay in the same address?
Yes (depending on the wallet, the steps might be different [not sure if all of the wallets, allow you to change it though]).
- Which wallet you're using?