Opening Bid: Two Clubs
This is a frequently used bid 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.
Four Diamonds - Five Clubs
With four diamonds and five clubs, opener should start with a 1 call and then rebid 2.
Five Diamonds - Five Clubs
With five diamonds and five clubs, most strong club systems use an opening bid of 2NT to show both minors. The KDbridge system prefers to use 3NT for 5-5 in the minors. (An opening bid of 2NT shows 5-5 in the majors.)
Responding to an Opening Two Club Call
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 forcing.
Negative Double by Opener
This is about the only place I can think of where the opener gets to use a negative double in a competitive auction... Suppose the opener bids 2 and responder asks about a 4-card major by bidding 2. then, suppose the next hand overcalls with a suit, for example by bidding 2, and opener has a 4-card heart suit... Seems like a perfect spot for the opener to use a negative double to show the other major.