What games are good depends on what kind of games you like. Got any ideas there? RPGs, strategy, puzzle, brain-teasers, minigames?
The wifi works a few different ways.
1. Ad-hoc with another DS in the same room. Some games allow you to share a single game card, however functionality is usually limited in this case. It is generally always better if both people have the game. In short, "sharing" a card for network play will give you a crippled gameplay experience, if it's even offered as an option.
2. Nintendo WiFi Connection. This lets you play over the Internet against other people. Everyone must have the game and an Internet connection. I have tried to make this work on an ad-hoc wireless network and been unsuccessful. It only seems to work if you have an "infrastructure" network, meaning you have a wireless access point. However, there is a Nintendo wireless USB device that supposedly gets around this. I have not tried it, so your mileage may vary.
