Crochet Beginner - can you look at my pic and tell me what I've done wrong?

[Pompelma]

I'm starting my second ever granny square (loving it).
However for the second time I can see I've messed up when switching colours.
The video I'm watching talks about grabbing the third (last in this case) chain loop once you've completed your round before adding in the new colour. I can see you're supposed to end up with two loops from the chain on your needle, before pulling through the new yarn but cannot figure out at all how you identify which is the correct chain or how to grab it correctly. Hence my dud red stitch sticking out like a sore thumb in the pic!
I need to see a close up of the stitch and a diagram or something of how to grab it. Can anyone help me? Or find me a link where this is explained? I've undone it so many times and can't get it right and I'm fed up googling!

Thank you

Well, I was ready to throw in the hook. But somehow I've done it, don't know how, can't explain, but I found a way that works for me!
Thanks for all your advice, links and pics!

Crap! I've just realised I forgot my last set of DCs! Ach...at least I know how to fix it this time.