Well you really shouldn't paste in the entire pattern, even when it's free. Yes, when a st number is given at the end of a row, that's how many you should have when you're done with it.
The cluster 2tog is explained right there in Row 2 -
"2nd row: Sl1. *[COLOR=DarkRed]K2tog. Do not slip sts off needle. K2togtbl into the same sts. Slip 2 sts off needle[/COLOR] – Cluster 2tog made." All of that, k2tog leave on needle, k2tog again tbl, that's the cluster.