In Japanese the ability to perform an action is expressed through conjugation of the verb, instead of by using auxiliary verbs like can and to be able to. This conjugation puts the verb into the potential form.

The potential form of all verbs ends in -る, and all potential forms are Group 2 verbs. Therefore, to convert a verb in potential form into -ます form, you simply replace the -る ending with -ます.

How the original verb is conjugated into the potential form depends on the verb group.

For verbs in Group 2, change the -る ending into -られる.

Group 2 verbs	食taべる	見miる
Potential form	食taべられる	見miられる
Polite potential form	食taべられます	見miられます
Translation	to be able to eat	to be able to see

For verbs in Group 1, change the final う-sound into an え-sound, and add -る as ending.

Group 1 verbs	行iく	話hanaす	飲noむ
Potential form	行iける	話hanaせる	飲noめる
Polite potential form	行iけます	話hanaせます	飲noめます
Translation	to be able to go	to be able to speak	to be able to drink

The potential forms of, する and 来kuる are special cases.

Special cases	する	来kuる
Potential form	できる	来koられる
Polite potential form	できます	来koられます
Translation	to be able to do	to be able to come

When using the potential form, what in English would be the object, is the subject in Japanese. Therefore you will see the subject particle が where you would expect the object particle を.

Breakdown of dekimasen.