3rd and 4th  Hand Openings :  1H/S-2C/D openings: open with 0-14 HCP instead of 10-14 HCP,  further bidding is identical as after normal opening: 0-11 HCP= minimum, 12-14 HCP= maximum. 

After Opponent interferes - All bids are the same as if there was no interference, double (up to 3S) is showing some bid that was blocked by interference, most often 1NT (after 1H/S) or 2D (after 2C) asking bids.

In competitive situations at level 3 or higher, after 1H-2D Openings/Overcalls when the second suit of opener is not known, bidding new suit by responder shows potential fit.

After Opponents Open (natural)–

Standard bidding, incl. Lebensohl over weak 2

After Opponents Open 1C (strong and artificial)

1NT 16-18 balanced,    double -takeout

other bids same as 3rd or 4th hand opening (see top of this page)

Other:

Cappeletti unless agreed otherwise.

Negative, support and responsive double up to 3S