I made an armature for a man, can I use that same armature for a female, clearing the weights and add another mesh in the place or do I need to make a new one?
You can absolutely reuse armatures among meshes, and doing so allows you to bring over NLA actions and other animations associated with the armature. It's not trivial to do this, since both meshes must be weight painted to the needs of the armature and bones... but since you will probably accumulate a lot of animations over time, it is a good investment for important characters, or those that have a lot of actions.
I use common armatures for sea turtles, fish, mosasaurs, dinosaurs of a common body plan, etc, and the whole mixamo concept is based on the idea that yo will accumulate and use common armatures.
Additional information: how to copy a rig to another mesh
Mixamo: https://www.mixamo.com/#/ -- Thgis is not Blender specific, but a handy way to see how others have animated particular sequences and their files will work with Blender. You would be downloading an FBX, and importing into Blender via File | Import FBX.
There is only one obstacle when reusing an armature - model proportions. It is very likely that the mesh you want the armature to be reused with has different joint placements and bone lengths (like trying to fit male armature to female mesh).
Let's say the meshes are very very similar. In this case the best thing to do is to skin an envelope, so the character mesh is completely inside the envelope mesh. The envelope is weight painted to the armature and the character uses Mesh Deform modifier to be driven by the envelope. When you switch the characters inside the envelope, you just bind it to the envelope and you don't weight paint the character. This saves work, but also might degrade the deformations compared to character driven directly with armature - it all depends how good the envelope mesh is.
Now let's say the meshes are different. If the armature is simple with not so complicated constraints on bones, you might be fine with just adjusting the armature to the right proportions in armature edit mode. Some constraints that take into account bone length, bone positions and rotations might break and you will have to fix them (setup again or reset them).
The ultimate way to approach this is to have scripts that build the complicated armature with all the drivers and constraints from a simple metarig. You adjust the metarig to fit the character, then just generate the rest. For example Rigify works like this.