Weak Two bids are premptive bids designed to create problems for the opponents. Unfortunately there is also a big potential to create problems for the players using them - unless they have had a serious prior discussion.
These bids are made on weak hands (less hcp than a 1 level opening). HCP should be in your long suits. If your second (minor) suit is 4 cards, a 5-4-3-1 shape is better than 5-4-2-2. You may pick up hands "between" a 1 opening and 2 opening and you need to decide how you will bid them. I do not rule out a void.
1. North opens 2D (weak 2 in major or strong balanced hand). East Doubles
Without East's X, South was required to bid (often 2H) so North had another chance to describe his hand. East's double has removed South's obligation to bid merely to relay back to North and any action now by South shows willingness to compete in the auction. Recommended is "System On". A 2H bid has its usual meaning (pass or correct) and additionally shows willingness and values to compete. In some defences, East's X (self-alerting) shows a takeout with shortage in S (2H (alertable) = shortage in H), so South may wish to enquire about this.
2. North opens 2D (weak 2 in major or strong balanced hand). South bids 2S
I hope you have discussed this 2S response with your partner because with the European Multi 2D the 2S response is correctible to 3H showing little more that three card heart support. In other systems it shows game interest if North's long suit is hearts. Big difference! It is alertable and opponents are entitled to a full explanation.
3. North opens 2D (weak 2 in major or strong balanced hand). South bids 3H
Another bid to discuss with partner before it happens. With the European Multi 2D this bid is preemptive and correctable to spades. Could be zero hcp. You may prefer another meaning but you need to have a partnership agreement.
4. North opens 2S (spades and minor 6-9 hcp). South responds 3C (or 3D)
Since 2NT is a transfer to the minor, 3C (or 3D) must mean partner wants to play in this contract. It is NOT correctable. North should pass. If you want this to have a different meaning have a prior discussion with your partner.