A jussive is a less common, 3rd person*, command-like assertion. Instead of commanding the person(s) being spoken to, a jussive commands a party which is being spoken of. This is easiest to understand via example.
imperative — “Eat your food.”
jussive — “Let him eat his food.”
You can see in the jussive example that the speaker is commanding something to be done, without speaking directly to the person who is to do it. In addition, note that we say “command-like” because the jussive does not carry the full force and strength of a command. For this reason, we have translated it “let him eat his food” and not “he must eat his food.”
There is no paradigm to present in the case of the jussive because it is identical to the imperfect form. That is, when you find an imperfect form, you will need to determine if it is jussive or not based upon context alone.
Finally, note that I have put an asterisk after “3rd person” above. The reason is that the jussive is also used in the 2nd person when there is a negated imperative. The Hebrew word to negate a command is אַל. While it is not the most pleasant passage to read, we find an example of an affirmed and negated 2nd person commands in Genesis 19:8. Here, Lot is attempting to appease the perverted men of Sodom. Note the imperative וַעֲשׂוּ (“and do”) and 2nd person jussive with the negation particle אַל־תַּעֲשׂוּ (“do not do”).