Irregular verbs in the Present Tense

querrer - to want
tener - to have
poder - to be able to (can)

The above verbs are known as stem changing verbs. That means that the stem (the part before the -ar, -er, or -ir) changes when the verb is conjugated. These verbs also happen to be shoe or boot verbs.

querrer is an e to ie stem changing verb.
So, change the querr- to quier-

Notice how the stem doesn't change in the nosotros and vosotros forms. This is where the name "shoe verb" comes from. The forms that have a change in the stem sort of make a shoe.

tener is also an e to ie stem changing verb.
So, change the ten- to tien-

The yo form of tener is also irregular.
The stem doesn't change and instead of just adding an -o, you have to add a -go.

poder is an o to ue stem changing verb.
So, change the pod- to pued-

A few verbs are extremely irregular.
ir - to go
ser - to be
estar - to be

To see the differences between ser and estar, see Lesson 8.