> So is there a nice tutorial which explains how to start mining using FPGA.

Not really, not a "starting from scratch" one.

> Or this is so complicated?

Yes, it is quite complicated - in order to work with FPGAs, some additional skills on top of software are required.  You need to understand logic design and some (fairly basic) electronics in order to make a successful FPGA.

However, as a learning project, if it's something that interests you, I'd say it's worth a go - you'll learn a lot, but it won't be a quick-and-easy learning experience :)

But start small - first off, write an FPGA which just flashes an LED on and off slowly - that enables you to learn lots of the low-level details without a complex logic design going on.  The FPGA equivalent of "Hello World"!