This example you posted I believe is likely done by sculpting but simulation may be faster here (for multiple good looking results with low experience. There were many major advances in the last year(s) of Blender development that are worth checking out if you aim for speed.
The steps you take and the ways you sculpt is completely up to you here.
In Blender 2.80+ you...
- Select the cloth (In object mode (switch with TAB or dropdown menu in the upper left corner of 3D viewport)
- Go to "Sculpting" workspace (at the top of the UI)
- Sculpt the surface to your liking. (with tools on the left - toggle by T, (NUM / to isolate selected object)
For older versions refer to Blender Wiki (Docs) here.
For basic and traditional sculpting I'd recommend starting with official Blender guide here and seeing sculpting walkthroughs in Blender and other software too (you can very well refer in this topic).
For cloth tool sculpting (new, faster) this might help you start.
By creating any shape(s) (mesh) for the cloth to collide against (e.g. during a fall) without making the collision shape(s) visible, you can create many seemingly random and beautiful folds and wrinkles.
I recommend seeing this short video for guidance (different scenario, same base method)