Need to know what type of flowers that are great for a small window bo

what is the lighting and exactly how big are the boxes

Here are some great ideas and inspiration:

https://www.homestratosphere.com/window-flower-boxes/

Try hanging petunias

I did tuberous begonias in window boxes last summer and they were beautiful and bright (I used orangey red and bright yellow ones). Easy to care for, they dead head themselves, all I did was water them after transplanting and fertilizing them.

You could probably use Lantana if they get lots of sun. They get tall, the flowers are small, but as they grow tall they will hang over edge of box.

Periwinkle or vincas go well very hardy, variety of colors. They don't have a deep root system, so should work well.

Geraniums and petunias in contrasting colors. The petunias will trail over and the geraniums stay upright.

Marigolds, geraniums, pansies...to name a few

annuals would be good - you can find a nice selection at any nursery. Depending on the size of box you may want to try some herbs too.