glass texture cycles


I’m using blender since 3 days and I create, tried to create :-), a glass cup like the nespresso one.

During render I see some black spots I don’t like! I tried to set the nor value but I’m not able to fix the problem.

see attache photo.

Can you help me?

I know this is just a simple project but I’ve to start to learn!:D:D

I want also to add coffee inside with typical espresso cream, like nespresso cup adv.

Do you know any tutorial Can I read?

thank you all for your help!