Traders do not always go all into their trading position, they divide their risk and enter incrementally. That is the concept of scaling in. Quite simple, but the methods on how you scale in can vary, you could use Fib levels, Pivot Points, Gann Lines, or any form of technical analysis, it is up to you.
Scaling out, as you could imagine is the opposite, getting out of your position the same way. Some traders, however, leave one scale out position infinitely. Whereby they keep a trailing stop to follow that position.