Gestern haben wir eine Wanderung gemacht.

This sentence is in the present perfect tense. In spoken German, this tense is generally used to express something that took place in the past.

The present perfect consists of two parts:

a) In second position in the sentence there is an auxiliary verb, usually the verb haben. It is conjugated as in the present tense.

b) The action that is being described in the sentence is expressed with the second verb, which comes at the end of the sentence. This verb takes a special form known as the past participle. Most past participles begins with the prefix ge-. In present perfect sentences, the past participle is an infinitive verb form, meaning it is not conjugated.

Present perfect: haben (conjugated) + past participle:

Was habt ihr gestern gemacht?
Wir haben eine Wanderung gemacht.