Ok if i buy 100 dollars on bitcoin and in the next days the bitcoin price goes way way down, will i lose my bitcoin can i just leave the bitcoin there for a year and wait till it gets the highest price and sell it?
do you ever lose your bitcoin if they go to low or you can just leave them there forever till they go high o price?
Pretty simple. You buy some BTC for 100USD and put those in your own wallet. There yout BTC is safe and you hold the private keys for those coins!
As long as you don't participate in trading on an exchange or sell your coins to other persons in private while the price starts to decrease, you don't make any loss! As long as you don't sale you don't make any losses!
So yes you can just hold for one year and hope the price will be higher than you have bought. Many people do so. So don't worry.
But nobody can predict the future. Maybe the coins will be worth less at that time. In that case you may hold a bit longer and just wait until the price starts to rise again and you're above your bought price and sell then.