Voir is a useful verb to know; it is irregular in the present, perfect and future tenses and therefore needs careful study.
Present Tense
Je vois I see, I am seeing
Tu vois you see, you are seeing (singular, familiar)
Il voit he/it sees, he/it is seeing
Elle voit she/it sees, she/it is seeing
Nous voyons we see, we are seeing
Vous voyez you see, you are seeing (polite, plural)
Ils voient they see, they are seeing (m)
Elles voient they see, they are seeing (f)
Perfect Tense
The past participle, 'vu', is irregular but not difficult to learn.
J'ai vu I have seen, I saw, I did see
Tu as vu you have seen, you saw, you did see
Il a vu he has seen, he saw, he did see
Elle a vu she has seen, she saw, she did see
Nous avons vu we have seen, we saw, we did see
Vous avez vu you have seen, you saw, you did see
Ils/Elles ont vu they have seen, they saw, they did see
Future Tense
Voir has an irregular stem in the future tense, and therefore the conditional tense as well. Here are some example sentences using the future tense.
Je verrai mes amis dimanche. - I shall see my friends on Sunday.
Tu verras tout ce soir. - You will see everything this evening.
Il verra le dentiste demain. - He will see the dentist tomorrow.
Elle verra ce qu'elle pourra faire. - She will see what she can do.
Nous verrons les pyramides en Egypte. - We will see the pyramids in Egypt.
Vous verrez ce que je veux dire. - You will see what I mean.
Ils/elles verront grandir les enfants. - They will see the children grow up.
Imperfect Tense
Voir is regular in the imperfect tense, so there should be no problems forming it. Here again are some example sentences.
Je voyais ma soeur le samedi. - I used to see my sister on Saturdays.
Tu voyais les enfants au parc. - You used to see the children at the park.
On voyait la mer de cette chambre. - We (could) see the sea from that room.
Nous voyions nos amis le weekend. - We used to see our friends at the weekend.
Vous voyiez toutes les expositions quand vous viviez en France. - You used to see all the exhibitions when you lived in France.
Ils/Elles voyaient deux ou trois films par semaine. - They used to see two or three films a week.
Conditional Tense
The stem of the conditional tense is of course the same as that of the future tense. Here it is, used in sentences.
Je vous verrais samedi si je pouvais. - I would see you on Saturday if I could.
Tu verrais ce que je voulais dire. - You would see what I meant.
Il verrait ses enfants plus souvent s'il habitait en ville. - He would see his children more often if he lived in town.
Nous verrions nos amis plus souvent s'ils habitaient en ville. - We would see our friends more often if they lived in town.
Vous verriez les oiseaux si vous restiez tranquils. - You would see the birds if you kept quiet.
Ils/elles verraient l'exposition s'ils restaient encore deux jours. - They would see the exhibition if they stayed two more days.
Present Subjunctive
Be careful in the present subjunctive of voir to use a letter i or a letter y as appropriate.
Il faut que je voie le dentiste. - I must see the dentist.
Je crois que tu voies mieux que moi. - I think you see better than me.
J'ai peur qu'il ne voie le cadeau. - I'm afraid that he will see the present.
Il va partir avant que nous le voyions. - He is going to leave before we see him.
Je veux que vous voyiez la vue de la montagne. - I want you to see the view from the mountain.
Il semble qu'ils voient la mer de leur appartement. - It seems that they see the sea from their flat.
Imperative
There is nothing irregular about the imperative of voir. As long as you know the present tense, you are unlikely to have a problem with the imperative.
Vois s'il y a de la moutarde. - See if there is any mustard.
Voyez l'exposition. - See the exhibition.
Voyons si on pourra le faire. - Let's see if we can do it.
Take care to learn this verb thoroughly, as it is of course commonly used. The future and conditional tenses are perhaps the trickiest.