Opening at the 2 level is not part of basic ACOL but it is preferable to opening a strong two. Opening 2 of a suit with a strong hand is safe but rare. It is much more common to have a long suit in a weak hand so a weak two opening bid can be used more often and it describes the hand accurately to your partner.
Weak twos have the added advantage of preempting the opposition and making it difficult for them to find a contract.
Opening at the 2 level shows 6 to 9 points and a six card suit. When using this bid, have at least two honours in your long suit (count the 10 as an honour if you have the Ace).
Don't make this bid if you are vulnerable because going down would be expensive.
Don't make this bid if you have a four card major suit. Opening 2 in a major makes it difficult for your partner to bid a 4 card major thereby missing a fit.
The opener at 2 level must not bid again. Any further action is decided by the responder.
The weak two bid is a preemptive bid like the weak 3 with a 7 card suit and the 4 level opener with an 8 card suit.
Overcalling a Weak Two
If a weak 2 is opened the following options are available to the overcaller:
With two stoppers in the opener's suit and a strong hand (16+), bid 2NT.
With a strong hand but no stoppers and with at least 3 cards in the other suits, bid a takeout double.
With opening points and at least three cards in each of the unbid suits, bid a takeout double.
With opening points or more and a long suit, bid the long suit.
With a rule of 20 hand, bid the longest suit.
With any other sort of hand, pass.