Let’s start at the very beginning.
To play a brass instrument you have to first breathe in and then blow vibrated air through the instrument. Your lips vibrate, it sounds easy but it isn’t!
Basic exercises we do every time we play.
Say 1,2,3 then breathe in through the mouth (like you are yawning) then blow the air out as if you are blowing through a straw. (using a straw will help)
Starts with step 1 + a floppy lip buzz
Starts with step 1 + an ordinary buzz
Starts with step 1 + a mouthpiece buzz