You may like this tutorial for simulating the flow in a deformable artery.
In this 1D example you can actually see how the fluid and the solid solver work and how preCICE couples them. Both a serial and a parallel version of the solvers are available.
As soon as you get some understanding of the basics, you can start building more complex simulations, using existing solvers. See this tutorial for example: FSI with SU2 and CalculiX.
If you have your own solvers, you can actually create your own adapter. As preCICE is free software, you can even modify preCICE itself to fit your needs.