What is the spell Alohomora?

It´s the spell to open closed doors

Alohomora is a spell to open locks on doors and so on.

A basic charm learned 由 first years use to unlock doors and so on

to unlock a locked door as seen in the Sorcerers stone used 由 Hermione.

It unocks doors. It's pretty much only useful with Muggle stuff, though, because wizards usually use magic to secure their doors.