Practice : There is / are . . .

Shounen ga imasu. : There is a boy.
shounen : boy
iru : there is / are...
(i-nai, i-masu, iru, iru-toki , ire-ba, iro ,iyou, ita)

Shoujo ga imasu. : There is a girl.
shoujo : girl

Otokonohito ga imasu : There is a man.
otoko : male
hito : man , human
eg. onnanohito : lady, woman

Niwatori ga imasu. : There is a hen.
niwatori : hen / chicken

Teeburu ga arimasu : There is a table
teeburu : table
aru : there is / are
(nai, ari-masu, aru, aru-toki, are-ba, are, (arou), atta)

Isu ga arimasu. : There is a chair.
isu : chair

Enpitsu ga arimasu : There is a pencil.
enpitsu : pencil

Pen ga arimasu. : There is a pen.
pen : pen (same!)

If you say " There is / are ..." for animals including human, "iru" is used. For "thing", "aru" is used.