In some churches, they are three-sided, in symbolism of the Holy Trinity. There are different ways of baptizing people, such as immersion, but at Trinity, we usually pour water on the baptized, also called affusion.
Sometimes you may see a baptismal font placed in the rear of a congregation's building. This is to remind believers of their baptism, and to invite them to place water on their head in remembrance of that sacred event. Ours is placed near the front of the church, a physical remembrance up front so that it is always in the line of view for the worshipper.
Baptismal Fonts in the Middle Ages sometimes had an entire room dedicated to their presence. Many of these fonts were designed for full immersion, and the room that would hold the font was a baptistery.
Regardless of the mode of baptism, all one needs is water and the word!