Poppins carries headlines and labels. Inter carries everything you actually read. Both load free from Google Fonts.
Use Poppins for anything that needs to grab attention — headlines, buttons, section titles.
Use Inter for body copy and anything meant to be read at length.
Set long paragraphs in Poppins — it's a display face and gets harder to read at body sizes.
Introduce a third typeface. Two is the system.