Opening Bid: Two Clubs - 11-16 HCP
This is an opening bid that is frequently used in all strong club systems... It shows an opening hand with a club suit. Players often modify it with different agreements, but the most common way of playing it is to have 11-16 HCP and at least a 5-card club suit. Some players prefer to promise a 6-card suit, but that agreement restricts the use of the bid. The opener may have a 4-card major.
Responding to an Opening Bid of Two Clubs
If responder uses the 2 asking bid and then rebids a major at the 3-level, the bid is natural with at least a 5-card suit and is forcing. (An immediate jump to the 3-level in a major is only invitational.)
Negative Double by Opener
Negative doubles are almost always used by the responder in a competitive auction, but it can be used by either partner after an opening bid of 2. If you are the opener, and your partner asks about a major by bidding 2, you might get an interference bid on your right. If they overcall with a major, you can double, promising the other major. If they overcall with a diamond bid, you can double to show both majors. (With only one, you should just bid it.) Partner is allowed to convert the negative double to penalty.
A jump to 4, the criss-cross minor, is Gerber asking for keycards. There are five key cards... four aces and the K, with only three kings.
Opening With Four Diamonds and Five Clubs
With four diamonds and five clubs, opener should start with a 1 call and then rebid 2.
Opening With Five Diamonds and Five Clubs
With 5-5 in the minors, or better, we use an opening bid of 3NT to show that hand. Most other club systems prefer a 2NT call, but we use that bid to show both majors. 3NT Opening Bid