You “tap a permanent for {C}” only if you activate a mana ability of that permanent that includes the {T} symbol in its cost, and only if it produces one or more {C} as it resolves.

If you tap a permanent for more than one {C}, you add only one additional {C}.

An ability that triggers when a player casts a spell resolves before the spell that caused it to trigger. It resolves even if that spell is countered.

Forsaken Monument’s last ability won’t trigger when you play a land.

A land is normally colorless, regardless of what colors of mana that land can produce. If an effect makes a colorless land into a creature without specifying that it becomes a certain color, the land creature gets +2/+2.