Regular Verbs in the Present Tense

In Spanish, there are 3 types of verbs:
Those that end in -ar, -er, and -ir.

First let's look at the -ar verbs.

estudiar - to study
necesitar - to need
nadar - to swim

In order to conjugate a verb, you drop the -ar and add one of the following endings:

Examples:
I swim: yo nado
you (informal, singular) swim: tú nadas
he swims: él nada
she studies: ella estudia
you (formal, singular) need: Ud. necesita
we need: nosotros necesitamos
you (informal, plural) study: vosotros estudiaís
they swim: ellos nadan
you (formal plural) need: necesitan

When you conjugate a verb, it's not always necessary to say the subject. For example, instead of saying "nosotros necesitamos" you can just say "necesitamos". The only time you really need to use the subject pronoun is when you're using the 3rd person. If you just said "estudia", you wouldn't be able to tell if he studies, she studies, or you (formal) studies.

Verbs in the present tense can be translated in two ways.
ellos nadan can mean "they swim" or "they are swimming"

Now let's look at the -er and -ir verbs.

escribir - to write
leer - to read
comer - to eat

These verbs share the same endings (except for the "we" form). So, in order to conjugate them, you drop the -er or the -ir and add one of the following endings:

I write: yo escribo
you (informal, singular) read: tú lees
he eats: él come
she read: ella lee
you (formal, singular) write: Ud. escribe
we eat: nosotros comemos
we write: nosotros escribimos
you (informal, plural) eat: vosotros comeís
they read: ellos leen
you (formal, plural) write: Uds. escriben

There are also some verbs that don't follow the usual rules when conjugating. See Lesson 7.