Q3 Answer
2 No Trumps
Your partner has overcalled and should have > 10 HCPs, 2 of top 3 honors in spades. You have stoppers in hearts and 13 points. This is enough to invite partner to game in 2 no trumps.
Q13 Answer
2 DIAMONDS
You have 10+HCPs your partner assumes that you have 4 hearts after their 1C bid. To tell them that you have 5 hearts you 'lie in a minor' by bidding 2D.
Q23 Answer
3 HEARTS
Your partner is saying that they have diamonds and 4 hearts. You can now add in 3 shortage points so bid 3H and invite to game.