How flank go held and played that trombone hurt my soul as a (former (I FUCKIBG HATED IT)) band kid that played trombone. You use two fingers for the slide, for starters.. you also don’t use your entire hand to hold that one part. I know how to hold it trust it just feels weird explaining it. Only one finger goes around the bar he was holding, I personally held two over the bar of the slide if I wasn’t playing (which I was ass at. Also my band instructor was just ass and wouldn’t help the kids that needed help and picked favorites).
A-Also if you need to like tense your lips like yer boutta give the worst head known to man for it to buzz right.