Porter describes what someone has on (il porte une veste), while mettre is the act of putting it on (je mets mon manteau). Mettre is irregular: je mets, tu mets, il met, nous mettons, vous mettez, ils mettent.
Examples
- Aujourd'hui, elle porte une robe bleue.
- Today she's wearing a blue dress.
- Mets ton manteau, il fait froid !
- Put your coat on, it's cold!
- Je mets un pull le soir.
- I put a jumper on in the evening.
The mistake to avoid
Porter also means "to carry", so il porte un sac can mean he is carrying a bag.
Where this fits in
Colours, clothes & likes, French A1: Name colours and clothes, buy something in the right size, and say what you like and don't like.