This tense is used more often than the simple past, especially in conversation, and is equivalent to I have asked or I asked.  Regular verbs use a form of haben or sein and a past participle.  Past participles are made by adding ge- to the beginning of the verb stem and -t (or -et, if stem ends in -t or -d) to the end.  

Sagen is to ask, and -sag- is the stem; therefore gesagt is the past participle.  
Arbeiten is to work, and -arbeit- is the stem; therefore gearbeitet is the past participle.
Machen is to do/make, and -mach- is the stem; therefore gemacht is the past participle.

Verbs ending in -ieren only add the -t ending.  Studieren is to study and studier- is the stem, so studiert is the past participle.  

The form of haben or sein is placed where the verb should be, and the past participle goes to the end of the sentence.  Ex:  Ich habe meinen Bruder gefragt - I asked my brother.

Haben or Sein

Most verbs use haben, but a few use sein, if and only if, both of these conditions are met:

1. The verb expresses motion or change of condition.

2. The verb is intransitive (i.e. cannot take a direct object.)

When modals are used in the present perfect tense with a dependent infinitive, the past participle is not used.  The infinitive of the modal acts as the past participle.  Logically, I had to go home would be translated as ich habe nach Hause gehen gemußt.  However, it is actually Ich habe nach Hause gehen müssen.  When there is no other infinitive in the sentence, then the past participles of the modals are used.  I had to would be translated as Ich habe gemußt.

All modals, as well as reflexive verbs, use haben instead of sein in the present perfect tense.  The reflexive pronouns follow the auxiliary verb as in Ich habe mir den Arm gebrochen.  I broke my arm.

With separable prefixes, the prefix comes before the ge- in a past participle, such as angekommen and aufgestanden.  From the participle of the base verb, and then add the prefix to the beginning.  But note that the prefix does change the entire meaning of the verb, and it may take a different auxiliary verb than its base verb.  For example, stehen takes haben, but aufstehen takes sein.

With inseparable prefixes, whether the verb is regular or irregular, there is no ge- prefix when forming the past participle, such as besucht and verloren.

To express something that has been going on or happening for a period of time, German using the present tense (rather than the past) and the word schon.  "I have been studying German for two years" translates to Ich studiere Deutsch schon zwei Jahre.