2 in 1 prams come with a chassis and a seat unit, which can be used from birth right through to approx 3 years. The seat unit can be used either forward facing or facing to the rear, so your newborn can face you from day one.
The 2 in 1 eliminates the need for a seperate carrycot as the seat unit will lay completely flat for you newborn, and then will have multi positions for your toddler. The seat units of your 2 in 1 come with adjustable calf supports, 5 point harness, large hood and a comfortable, usually padded seat unit.
The 2 in 1 is not suitable for your baby to sleep in over night as the sides are not deep enough to allow for a mattress. If this is a required option you would need to consider the 3 in 1 which comes with a carrycot as standard.