They are different forms of the same verb, called conjugations. Verbs conjugate to match the person doing them. For example, I can say "I am" but not 'you am' - I need to change the verb to match, i.e. "you are". It's like that in German too, but with a few more forms.
er/sie/es schreibt = "he/she/it writes"
ich schreibe = "I write"
Note also that it's not necessary to capitalise German verbs - only nouns always need a capital letter.