Lots of great answers here,. The cycle is a little bit like this:
1. Naive B cells released from Bone Marrow travel to various lymph nodes and other lympathic organs.
2. Meanwhile, Dendritic Cells capture a pathogen, degrade it and present the antigen on it's surface. Note: Only professional APC's can do this because they have MHCII's. (3 APC's: Dendritic Cells, Macrophages, B-Cells). T cells are not a professional APC (lack MHCII). Generally of the three APC's, dendritic cells do this most frequently.
3. Dendritic Cell travels to nearest lymph node where it awaits the naive T helper cell (specific to its antigen). Upon interacting, dendritic cells release cytokines that activate the naive T cell and allow it to differentiate into a specific type of T helper cell (there are various sub-types: TH1, TH2, etc.)
4. The activated T cell then leaves the lymph node in search of a naive B cell in other nodes.
5. Eventually, naive B cell becomes activated and is stimulated to produce an army of memory B cells and Plasma Cells (after differentiation).
6. These plasma cells will exit the lymph node into the blood plasma, where they begin secreting Ab's. They also travel to the bone marrow and other lymphatic tissues and organs and begin secreting Ab's there as well.