このペンを使っていいですよ。

this (something or someone close to the speaker (including the speaker), or ideas expressed by the speaker)

pen

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 use (a thing, method, etc.); to make use of; to put to use; to use (a person, animal, puppet, etc.); to employ; to handle; to manage; to manipulate; to use (time, money, etc.); to spend; to consume; to use (language); to speak

good; excellent; fine; nice; pleasant; agreeable; sufficient (can be used to turn down an offer); ready; prepared; profitable (e.g. deal, business offer, etc.); beneficial; OK

be; is

indicates certainty, emphasis, contempt, request, etc.; used when calling out to someone; used to catch one's breath or get someone's attention; yo!