Here are some examples of how you might use "tant mieux":
* "J'ai trouvé un emploi bien payé. Tant mieux!" (I found a well-paying job. So much the better!)
* "Le temps est beau aujourd'hui. Tant mieux pour la randonnée." (The weather is beautiful today. All the better for the hike.)
* "Il a décidé de venir avec nous. Tant mieux!" (He decided to come with us. So much the better!)
Essentially, "tant mieux" is used to express that something is good, and you're happy about it.