Assign footprint to symbol removes symbol

[der.ule]

This links should get you started:

• Tutorial: How to make a symbol (KiCad v5.1.x)
• Library management in KiCad version 5
• Tutorial: How to make a footprint in KiCad 5.1.x (From scratch)?

Basically almost anything written by @Rene_Poschl should be read if you are a beginner