I'll be gentle...!
The Blu-Ray player has both High Definition Pictures, and Hi Definition Audio. Your TV (if it's a new one) will most likely display High Definition picture. You will need a HDMI lead to take the picture to the screen.
Your home theatre (assume it's an all-in-one DVD player/amplifier) should have (but check it first) either an optical (toslink) or digitial coaxial input. Using one or other of these inputs, you can take the dolby digital sound track (but not the newer, HD audio soundtrack - it can only travel over HDMI cables) to your amplifier.
When it comes to digitial cables, there is a lot of debate as to whether more expensive means much better - personally, unless you have a very expensive system or long cable-runs, it's probably best not to spend too much money on them. Get some from a reputable manufacturer (of cables, rather than of, say, televisions).
If I have over (or under) simplified, let me know.