Searching Telegram groups is quite easy. Let me explain you step by step.
Step 1: First you will have a search icon on the top right side, click on it. (IMAGE 1)
Step 2: Then type your keywords (IMAGE 2)
As soon as you proceed by typing your keywords, telegram will search accordingly.
Telegram will show you a list of some public channels in the results.
Telegram will show you a list of 2 or 3 channels.
If you want to join those groups then you can join easily by clicking.