Then versus Than; To, too, or two.

These are two of the errors I see made too frequently when we wish to express ourselves now and then, but pick the wrong one rather than the right one (or two).

"To" is a preposition and an infinitive marker:
I want to go to the store.
"Too" is an adverb:
This is too much fun. [Here it is used to modify "much".]
I, too, want to go to the store. [Here it means "also."]
"Two" is a cardinal number (as opposed to an ordinal number, as second, not as opposed to a Bishop or Pope):
I too want to go to two stores.

"Then" is an adverb of time:

I like to go to the store now and then, too.

"Than" is a conjunction and a proposition:

I would rather go to the store with you than by myself.

I know you are smarter than I.