Spanish verbs ending in -gar replace the -g- with a -gu- in El Presente de Subjuntivo. This is to preserve the sound from the infinitive.
Here is the conjugation of pagar (to pay) affected by this spelling change:
|él / ella / Ud.||pague|
|ellos / ellas / Uds.||paguen|
Read and listen to these examples:
There are other useful verbs that have this same g > gu spelling change, for example: apagar (to turn off), entregar (to deliver), jugar (to play)
Here are more examples with these verbs: