Conventional strollers usually have a forward-facing, fixed seat built into the stroller. For conventional strollers that accept infant seats, the infant seat attaches parent facing so you can maintain eye contact with your baby.
Modular strollers have seats that can be installed in different directions so that your child can ride either forward- or parent-facing, a popular option for some parents. However, since a modular stroller has multiple configurations, there may be more individual components or adapters to keep track of.