1. Used to refer to somethng or someone separate and different from the signer and the person they are signing to. If the thing or other person is real and located in the situation, then you point to where it/he/she is located, otherwise you point to where you imagine it/he/she is located. When the pointing sign is made immediately before or after a verb sign, you usually mean that the thing or the other person does the action of the verb, or is affected by the action of the verb. English = it (thing); he, him (male); she, her (female).
2. Used to refer to a location or time that is not near either the signer or the person addressed. English = there (location), then (time).
3. Used to refer to some other but particular and special thing or person and is used alone or next to a noun. The signer expects the addressee to know which one. English = the, this, that.