Sign languages use the unique features of the visual medium, but may also exploit physical features. Mostly, spoken language is linear so that you can make or receive only one sound at a time. On the flip side, sign language is visual. You can use a simultaneous expression, although this is limited to articulatory and linguistically. Visual perception enables the processing of parallel information.
The sentences or clauses in a language have a specific structure. If you compare languages to each other, you will see that differences in structure emerge. For instance, in English, we have the Subject then Verb then Object:
I(S) baked(V) a cake(O)
In BSL, the concept is different. It starts a sentence with Time-frame then Topic then Action or a Comment.
Yesterday(time frame) cake (topic) baked (action/comment)
It is essential to have the time-frame in BSL. The signs in sign language do not change according to the past, present, or future. Whereas in English, we show the time-frame by using a variety of words (made, make, building, etc.).