Most of the time we use adverbs to describe verbs, because we're describing how we're doing something:

I slammed the door angrily.

However, if we're describing how someone feels, or how something looks, sounds, or tastes, we use an adjective, because we're describing that thing.

The food tastes delicious - not deliciously

The ring looks expensive - not expensively

I feel happy - not happily

Look can also be followed by an adverb if I say something like

look at these sentences carefully - because it's the way in which I want you to look.

These sentences look difficult - here we need an adjective, because I'm describing how the sentences look to me.

This episode's page on my website can be found here:

https://englishwithkirsty.com/podcast/episode143