Many girls have the same abilities or close abilities. If you put them in the same team, it will be more efficient.
For example, girls like Convalaria, German Iris or Gerbera have a bonus to solar blast damage. If you make a team with her, you willget a solar blast bonus of 65% (if I'm not wrong). Add girls like Bipinna Cosmos and Strawberry Candle who have a shine crystal drop bonus and you get a team with a really strong Solar Blast they can use more frequently.
Take girls like Rose, Snapdragon and Anemone. They all have a counterattack ability based on their defence. Add girls with defense bonus and you will get a good counterattack team.

For skills, it's the same thing. Pair girls like Convalaria or Toad Lily with a 3 target skill and pair them with Cyrtanthus and Justicia (who have a x1.2 skill rate bonus based on affection for the whole team) and you will have a nice skill-spam team with good multiple-target skill. As (th girl you can add one like Iris to get even more damage bonus (Toad Lily and Justicia already have one).

After that, you also need tomake teams with what you have. If you don't have any counterattack girl, don't even try to make a counter team.

Another example, based on your team, your Bride Cactace will work very well with a girl like Anthurium with her +22% damage on &st turn. Since Bride Cactace already give a skill rate bonus.
Another one, the current reissue Girl, Moonvine will give you a x1.2 skill rate bonus on the 3rd turn. The next reissue girl, Tachibana do the same thing on her evolved form. And the next next reissue girl is Star Lily with her +15% damage on 3rd turn. These three vork wery well?

That almost what I mean when I spoke about synergy between girls. And it's also almost the main topic of this thread ^^. You certainly can found a lot of ideas in it. But it mainly for slightly more advanced players with more girls. For a beginer, already try to do with what you have and good luck for gacha ^^.