That was a basic thing in trading you need to buy low and sell it when the price is high.. do you think you can make profit if you buy high and sell it for lower price?
so before you can make profit if you buy low you should sell it for the high price... and the movement for example bitcoin the price of bitcoin is not stable anytime soon the price can be increase or down.. depending in demand and supply
In trading if you want to learn better to start to learn how to make your own margin and sell bitcoin as sample 25% if the price was increase today and makes your profit if the price tommorow will increase sell 50% of your bitcoin so that you have a remaining of 25% of bitcoin that you can sell if the price continues to increase in order to make profit..
If not increasing just wait again or if the price is down wait for more cheaper price and buy more bitcoins and do the same if the price increase just sell partially in your bitcoin so that you will not loss opportunity to make profit for every price increase..