Have some questions about some teeth shifting as i don't know much. can it cause pain, discomfort, huge gaps?

Not right away: But you should find out why they are shifting and do something about it before it comes to those things.

Yes, yes, & yes: There's a reason for the shifting such as gum/bone disease, previously extracted teeth that were not replaced, malocclusion, parafunctional habits, and other reasons. See your Dentist. The cause must be treated to prevent further shifting. Referral to Periodontist and/or Orthodontist may be required before any restorative treatment is accomplished.