Definition: used to refer to a person, object, idea, etc. that is separated from the speaker by space or time; used to refer to something that has been mentioned or was involved earlier, or to something that is already known about.
Pronunciation (production): Dominant "Y" (handshape), palm generally down (orientation), in space (location), moves downward (movement).
Grammar: The THAT sign may be inflected with the subject-determiner agreement.
Pronunciation (production): Dominant "Y" (handshape), palm generally down (orientation), moves downward (movement) onto the non-dominant flat-B with palm up (location).
Formal citation; the passive palm in this ASL sign is not frequently used, usually signing THAT without the passive hand. Signing THAT with the passive palm may be used in some circumstances. E.g. "IX-he TOLD ME THAT [emphasis]..." Or, "THAT's WHY".
First 100 words.
As you feel more comfortable with the first few hundreds of ASL signs, progress further with your vocabulary and learn signing more.