Breastfeeding and formula ‼️⁉️

Has anyone breastfeed then Switched to formula? If so how did you make the transition? Also my baby is super picky with bottles at first she would take a bottle ( Comotomo ) around 2 months and one day she just absolutely refused. She is now three months and I would like to introduce formula but I also don’t even know how to pick a formula out??? What are the differences?? Can anyone help me out please?