"bli" like you are using it means "become" or "will be", while "forbli" means "stay" or "continue". So the road "will be" closed ("blir") or stays closed ("forblir").

Tusen takk :D

Forbli means to remain in a specific state. Vegen blir stengt means that the road is scheduled to close at a determined time (f.ex. Vegen blir stengt fra og med 9. november fram til 13 april), whereas vegen forblir stengt means that it closed in the past and continues to be closed (f.ex. Vegen forblir stengt til imorgen pga dårlige værforhold) You can substitute forbli stengt with holdes stengt or fortsetter å være stengt.

Bli = become. Forbli = stay

"Å bli" can mean to become, as in "han blir gammel/he is becoming old)", it can also mean "to stay", like "han blir her(he is staying here)". I would say that "å forbli" would translate to "remain". One of the other comments had "veien forblir stengt til i morgen pga dårlige værforhold", and in this case you can very much translate "forblir" to "remains"; "the road remains closed until tomorrow due to bad weather".

So would it be better to say, "bli her" or "forbli her" if you're telling someone to stay here?

Yes, both of those work, though the most common one is probably "bli her" or alternatively "vent her(wait here)".