First of all, welcome to quilting! You will quickly find yourself addicted to this site, and the people on here are so very helpful.
Straight of grain vs. bias:
When you hold the fabric with the selvage on the top, like a square, straight of grain is in a north-south or east-west direction. Bias is a northeast-southwest or northwest-southeast direction. The bias will also have more stretch to it, which is great for some applications, but basic quilt squares (esp triangles as at least one side will always be on the bias) may stretch a tad when sewing.
My non-quilting mother always told me the more you pin, the more stable it remains, so don't be afraid to pin...
And good luck! Enjoy and allow yourself to make mistakes, that's how we learn. Make a practice piece for new techniques, save them and put them together for a quilt for yourself - what fun to look back at your early work!