What aspects of the FPGA do you want to learn - RTL/VHDL/Verilog coding, designing hardware around it.... it's a pretty big topic, focus on one area first. If you want to learn coding, look at the e-books on this site - I like hdl-chip coding personally.
and the list goes on, make a search of EDAboard forum with "FPGA" AND "learn" as keywords and you'll get a long extensive list that will answer your question.
The way I am learning about FPGA is the following:
First study VHDL (system design by VHDL (or something like that ) downloaded from edaboard)
Then some tutorials concerning FPGA technology on the internet
then the book Digital SIgnal processing with FPGA (downloaded somewhere from EDABOARD)