“vermissen” is what you do with things or beings that are not there. “fehlen” is what the things do. They can both be used to express that you miss someone, but the phrasings are different.
- Ich vermisse dich.
- I miss you.
- Du fehlst mir.
- I miss you.
For more examples and other uses of fehlen, make sure not to miss my article on that here :)

Sehr gut.Danke
Gerne :)!