Let me quote a classic scenario in order to understand how the price or what affects Bitcoins.
There are a fixed amount of Bitcoins already made, no one can made another Bitcoins.
So as there is a fixed amount of Bitcoins or let’s say the supply is limited.
If the supply is limited and the demand is high, then in order to fulfil the demand the price will go high.
Reverse happen, if the demand is less and supply is good, then the price will go down.
This also happens with Bitcoins for which the price affects.
If you have some more doubts then i will be glad to help you out.