This guide will tell you in detail and clearly show you how to enable the beta test and how to enable modifications from the Workshop

1) In the Steam library, right-click on the game and select Properties
2) Go to the Beta subsection
3)Enter koboldyipyap in an empty line
4)Click check the code
5)Click the blue button to join: beta
6) Go to the workshop and choose the modifications you are interested in
7) Launch the game
8) In the game, click the settings button
9)In the modifications tab, click the checkboxes for your modifications
10)In the mods settings section, you can delete or leave the suggested functions
11)Click play and choose a level

P.S: sorry in advance for the bad еnglish)