The Perfect Tense with "sein"
While most German verbs form the perfect tense using a conjugated form of haben, verbs that describe a movement from one place to another use sein (to be) as their helping verb.
Conjugate sein to match the subject (ich bin, du bist, er ist, etc.), and put the past participle at the end of the sentence.
Hiking (wandern) is also a form of motion from one place to another, so it takes sein.
Events and Changes of State
Verbs that express an event occurring or a change of state also take sein. A very common example is passieren (to happen).
Remember that verbs ending in -ieren do not take the ge- prefix in their past participle. The past participle of passieren is simply passiert.
Separable Verbs of Motion
When a verb of motion has a separable prefix, the whole verb still uses sein. In the past participle, the -ge- is sandwiched between the prefix and the verb stem.
For example, kommen (to come) is a verb of motion. So is zurückkommen (to come back), and its past participle becomes zurückgekommen.
The same applies to boarding and getting off vehicles: einsteigen becomes eingestiegen, and aussteigen becomes ausgestiegen.
Whether you are walking, driving, or flying (fliegen), if you are traveling from point A to point B, use sein!
