how to insert vertex in a face? and that the face is divided forming other faces
Use poke faces
From the blender manual:
Splits each selected faces into a triangle fan, create a new center vertex and create triangles between original face edges and new center vertex. The Offset can be used to make spikes or depressions.
You can then choose to offset the newly created vertex.
In versions previous to blender 2.8 the shortcut is ⎇ Alt + P.
In Edit Mode, select only the Face you want to divide. Click Subdivide.
This divides only the selected face rather than the entire object.
The difference between this and the Poke Faces method is that instead of dividing the face into a triangle fan, it divides the edges rather than dividing at the vertices.