hanamaru
Say what you have
ペンが あります is both “there is a pen” and “I have a pen”. Japanese does not split having from existing. Living beings take います.
JLPTN5
thing + が あります (I have)~ ga arimasu
There is no separate verb for “have”. What you have exists, and what exists stands with が: ペンが あります, I have a pen; じかんが あります, I have time; おかねが ありません, I have no money. Who has it goes first with は: わたしは ねこが います.
Things and ideas take あります, people and animals take います — the same choice as when you say where something is. The question is the same sentence with か: ペンが ありますか. The answer can be just あります or ありません.