I have a clock in my class at school.

The verb for "to have" is avoir. In the present tense, study the first box:
French verb conjugation: avoir (http://www.french-linguistics.co.uk/verbs/table/avoir.html)

Don't use online translates, they are not correct.
To say I have a clock at my school would be:
J'ai une horloge à l'ecole.
What level of french are you?