*NEWB* Struggling with mates in assembly

Hello everyone, basically for the Irish state exams there is a subject where we have been assigned the task of "Generate computer model, comprising at least 5 parts, an Assembly, Drawing and an eDrawing of the selected artefact." The artifact is a computer mouse and I modeled it in one part and then inserted each solid body into a separate part and now I am struggling with the assembly. When I select two faces I would like to mate all the mate options are grayed out.

[rant]I am only asking you people of the internet as the deadline is very soon and I cannot access the teacher due to the holidays. It is quite stupid that we have to use Solidworks when we don't have any kind of book or tuition in using it.[rant over]

I'm not sure if I should use the create assembly from part option because I probably will be failed for not meeting the requirement of at least 5 parts.

Thanks in advance for any help you can provide.

The parts I want to mate are the two side parts to the base and then the top body.

Message was edited by: Daire Vickers Fixed typos, added pictures and paragraphed for clarity.

Message was edited by: Daire Vickers: Removed the attached file in case any other students try plagiarize my work.

SolidworksAssemblies