Hi, I don´t speak english so sorry if you can´t understand my question
 I´m relatively new in the world of music production, and still learning about terms for effects, kinds of sounds and that kind of stuffs, but there is one sound or group of sounds that i don´t know how to call them, I mean that part between the melody and the drop.
I´ve heard them called ¨Breakdown¨ or ¨Drum fills¨ sometimes this transitions are made with drums or a sound effect I know that but...

How i can find them in youtube? They had another name? How can i made that transition effect?

Thanks for answering

To make any effect, is the same way you make any sound. You first have to come up with the concept of what you're trying to do (the sound that the effect is based on) and then actually apply and effect unit to the sound. Couple that with some automation (or self modulation) [how the effect/sound exist and evolve over time] gives you an effect.

I also suggest having these effects as a separate channel in your mix because it gives you a little more control over how much of a presence (or volume change) you want it to have as it continues into the next section.

I suggest start making stuff as creatively as possible. It doesn't have to make to much sense because it's a transition or a "fill".

There's also musical transition on top of the sound transition.

I like to use delays, reverbs, chorus, flangers, phasers, filters, synth automation, drum fills to pick up into the next parts of the song.

Hope this helps.

Buildup is the term. Also if your just getting into producing look up how to make Risers, Sweeps, and Pads. All of those are used for Buildups