High-level synthesis (HLS) has been gaining traction recently as a design methodology for FPGAs, with the promise of raising the productivity of FPGA hardware designers, and ultimately, opening the door to the use of FPGAs as computing devices targetable by software engineers. In this tutorial, we introduce LegUp, an open-source HLS tool for FPGAs developed at the University of Toronto. With LegUp, a user can compile a C program completely to hardware, or alternately, he/she can choose to compile the program to a hybrid hardware/software system comprising a processor along with one or more accelerators. LegUp supports the synthesis of most of the C language to hardware, including loops, structs, multi-dimensional arrays, pointer arithmetic, and floating point operations. The LegUp distribution includes the CHStone HLS benchmark suite, as well as a test suite and associated infrastructure for measuring quality of results, and for verifying the functionality of LegUp-generated circuits. LegUp is freely downloadable at www.legup.org, providing a powerful platform that can be leveraged for new high-level synthesis research.