long bow "not proficient" what does it mean?

[BlackViper]

i know it means "my caracter cant use it properly cause he/she is not trained in it"..
but, if i use a bow anyway "even though he is a necro and dont really use it more then nessesary". what do i lose?.. does it just make less dmg then it says it would? or do i lose soomething when using my magical skills aswell that ofc has nothing to do with the bow cause that is in my 2nd hand. not my main weapon.

[Ashe]

It's less damaging, harder to hit with and you don't have access to the weapon skills that come with it.

[Zygfryd]

Pretty sure you get general Disadvantage on rolls if you have equipped something you lack proficiency for. At least that's what it looked like when I was wearing the wrong kind of armor.

[darkbird1000]

in 5e longbow is martial weapon in other dnd vers bows were a weapon class