You need a six card suit in diamonds, hearts or spades
You need 6 points in the suit (Jan)
You need two of the top three honours or three of the top five. 8 - 10 points when vulnerable. You can cut a few corners not vulnerable. (Jane)
You will see other people do it but you should not open a weak two with a weak suit and defence. e;g; S:Axx H:Axx D:JTxxxx, C:x
Do NOT open a weak two with a void. (Jane's teacher says so, I do what he tells me)
Do NOT open a weak two in first or second seat if you have a four card Major as you may miss a golden fit.
Opening a weak two is a preemptive bid you should not bid again unless partner forces you to do so. e.g. by bidding 2NT or 4NT.
Bidding after the weak two bid.
If you have about 10 scattered points and 3 of partner's suit raise to the 3 level to make it difficult for the opponents. This is not asking opener if they want to go to game.
You need an opening hand plus if you are responder to bid 2NT
2Nt is used by responder to find out if you have a maximum or a minimum for your weak two.
With 8 -10 points and two of the top three honours when partner bids 2NT you bid an ace or king in another suit. With <8 points re-bid your original suit
With AKQxxx in your suit bid 3NT. This tells responder exactly what you have and they can decide if they want to play 3NT or go to four of your major.