手紙に切手を貼るのを忘れるな。

letter

at (place, time); in; on; during; to (direction, state); toward; into; for (purpose); because of (reason); for; with; by; from; as (i.e. in the role of); per; in; for; a (e.g. "once a month"); and; in addition to; if; although

stamp (postage); merchandise certificate

indicates direct object of action; indicates subject of causative expression; indicates an area traversed; indicates time (period) over which action takes place; indicates point of departure or separation of action; indicates object of desire, like, hate, etc.

to stick; to paste; to affix; to link (e.g. in WWW forums); to stretch; to spread; to strain; to tighten; to put up (tent); to form (e.g. ice on a pond); to fill; to swell; to stick out; to put; to slap; to be expensive; to become one tile away from completion

indicates possessive; nominalizes verbs and adjectives; substitutes for "ga" in subordinate phrases; (at sentence-end, falling tone) indicates a confident conclusion; (at sentence-end) indicates emotional emphasis; (at sentence-end, rising tone) indicates question

to forget; to leave carelessly; to be forgetful of; to forget about; to forget (an article)

(sentence end, mainly masc.) indicates emotion or emphasis; (used with masu stem verb) command; (used with dictionary form verb) prohibition