Below are a bunch of videos that can help you understand the main principles of making different styles of mould for lots of different casting materials and processes. There are many different methods for creating moulds depending on lots of factors, so to make sure you're on the right track it is still worth speaking to Emily in Alternative Materials to doublecheck whether the method you are looking into is right for your object/project. The videos below are meant to help give an initial understanding so you feel more confident moving forward for your own work. (p.s. 'Mold' is simply the US spelling of 'mould'.)
Silicone mouldmaking
Epoxy resin
Plaster moulds for slipcasting
Slipcasting
Metal-effect casting (a.k.a. 'cold casting')
3D-printed moulds (FDM)
Paper pulp-forming from 3D-printed compression moulds
Rotocasting (produce lightweight, hollow casts)
Credits:
Created with an image by prakasitlalao - "white glass fiber composite hand lay up raw material background"