Simultaneous action is designated by replacing the "〜ます" ending of the polite present positive tense of the first verb with "〜ながら". The tense is then determined by the latter verb. Both actions should be performed by the same person.
Those more comfortable thinking in terms of the dictionary form can see this as adding "〜ながら" to the stem of vowel-stem verbs, or the い-row of consonant-stem verbs (e.g. 飲む -> 飲みながら example below). The irregular verbs are also put in the い-row making them identical to the consontant-stem verbs.
<vowel-stem verb stem>
ながら <second verb>
<consonant-stem verb stem in い-row>
The tense of the sentence is given with the second verb.