How to count things.
when you count something like apple, egg, watch, bag, you say like...
１つ（ひとつ）/ 1
２つ（ふたつ）/ 2
３つ（みっつ）/ 3
４つ（よっつ）/ 4
５つ（いつつ）/ 5
６つ（むっつ）/ 6
７つ（ななつ）/ 7
８つ（やっつ）/ 8
９つ（ここのつ）/ 9
１０つ（とお）/ 10
This is different way to count number itsself.
７つ あります。
means "there is 7.". this doesn't mention what exists, but only mention how many there are. It's ok to say this sentence. It's correct.
てーぶるが ７つ あります。
"てーぶる/table". so it means "There are 7 tables".
かいぎしつに てーぶるが ７つ あります。
"かいぎしつ/meeting room". so, it means "There are 7 tables in the meeting room".
