When I'm doing pull-ups I feel them in my shoulders and not in my arms. What do you think about it? I'm not doing them right? I also focus on keep my shoulders down and make the scapular retractions but it feels to difficult for me... I don't want to get injured or something like that. Any advice?

If you are feeling it in the posterior deltoid aspect of the shoulder this is to be expected as the posterior deltoid extends the shoulder and this is created during a pull up. You may be feeling it here as it is a weak area. When you do a pull up there is no need to retract and depress your shoulder girdle throughout the movement. You will naturally retract as you pull up as you will use your rhomboids and middle trapezius to help create the pull up motion. Although pull ups are a great bicep builder you won't get the same feeling in the bicep as you are not isolating them to create the movement unlike you are in a bicep curl for example. Also if you want to create more bicep recruitment you need to do do chin ups not pull ups. The difference is when you do a pull up you use a pronated grip which means your palms are facing away from you. A chin up is when you use a supinated grip which means your palms are facing you.

It might be a good idea to start with some other latt exercises like a basic latt pulldown on a cable machine. Since this is a little more basic, you should be able to focus on your latts as your pulling down. Latt pull downs are also good for improving your pull-ups. Just make sure you are not swinging your body. Check out some videos by Scott on this:)

Look in the mirror, if you see a pump after doing them then your lats are being worked. When I do my pull ups, I never feel a burn in my lats but I know its getting work because I see a pump, and I kinda feel the lats pushing against my arms.