If you’ve read a tutorial about the subject, you’ll know what i’m going to talk.
Select your mesh, go to F9 and in “Link and materials” pannel and you’ll see several buttons together.
The first one says how many indices (number of materials you have in an object, aldo you can have the same material in more than 1 indice “max = 16”). If you have “0 mat 0” you have no materials in your mesh.
To put 2 materials in your mesh do this:
(using a new created object with no materials assigned)
1 - Click twice on New (Link and materials pannel). The first time it’ll create a material and second time it give a new indice but with same material (the “2” on the left says how many indices you have in your mesh, the “2” on the right say you are in indice 2).
2 - Change to F5 (materials pannel). Below the materials name you’ll see the same (2 mat 2). Again, we have 2 indices and we are at indice number 2.
3 - Create a new material and change the color. Now indice 2 have a diferent material, we just have to say to what faces it will be applied.
4 - Go back to F9, enter editmode in your mesh and select the faces that will get the new material. Go to “Link and materials” pannel and press “Assign”.
That’s it! A mesh with 2 materials!