Hello .As explained above,your teeth might be having plaque and calculus(yellowish deposits) which needs to get cleaned professionally through a procedure known as scaling.It might be because of fluorosis too (excess fluorine content in water)
After cleaning,bleaching is required.
Regarding zigzag teeth ,they are malaligned
Next Steps
Visit to the dentist and get scaling done(oral hygiene prohylaxis)
For malaligned teeth braces are required or you can go for smile designing too
Health Tips
Do twice brushing and floasing.you can buy a home bleaching kit too