It requires proper training and practice to be good at pattern making. The truth is, not all designers are adept at this. Some of them hire pattern makers so they can focus on designing instead.
You can choose to do this and you can have your production house do it for you. If you prefer to do it, the first step is for you to make block patterns or simple patterns for your basic clothing pieces like a shirt, trousers, and skirt. Build a library of patterns for different pieces to save you time and effort.
To draft by hand drawing, you need to work on a large table. Use kraft paper or Manila paper, a set square (i.e. an L-shaped ruler), and a set of French curves to make smooth curves for sleeves, hips, and more. Trace the pattern, cut it out, and pin it on your fabric for cutting. The following are good references to help you get started Pattern making for Fashion Design, Principles of Flat-Pattern Design, and How Patterns Work.
To draft using a computer, use a CAD (computer-aided design) fashion software. It’s more beneficial to do this because it will take you less time to reproduce and finish the patterns. It will also spare you from costly mistakes in measurements.
Draping is simply using putting a long piece of fabric over a dummy model and pinning it to get the different measurements and patterns you need for a garment. Get an adjustable dressmaker’s dummy so you can adjust the shoulders, bust, waist, and hips. Once you’re done with your patterns you can now start working on your sample and collection!