Efficiency in this scenario is telling beertools how much sugars your system can extract from the grains. 75% is a pretty good starting percentage, with some tweaks it will rise above that a bit. However due to problems with grain crush, sparging techniques, and so on you will never get 100 percent of the goodies from your grain. If you were able to extract 100 percent of the sugar from the grain, you'd need less grain to hit your gravity. So basically as your efficiency goes down, beertools compensates by making you add more grain to get to the target OG.
You can determine is 75% is right by dividing your actual post-boil gravity by the OG predicted by beertools, in this case 1.067. If your answer is below one, your efficiency is worse than 75%, answer is extremely close or is 1, your efficiency IS 75%, and if it's over 1 your efficiency is greater than 75%.
One way to calculate your efficiency exactly is to set your efficiency to 100 percent in beer tools after the recipe has already been set. It will jack your expected OG way up. Then take your real OG reading and divide it by beertools expected OG and multiply by 100. That will give you your actual efficiency.
Attenuation is the percentage of sugars your yeasties will eat.
http://www.wyeastlab.com/rw_yeaststrain_detail.cfm?ID=5
That yeast has an expected attenuation of 73-77 percent, meaning that percent of the sugars will be consumed. Some yeasts like champagne can eat 100 percent leaving an extremely dry liquid. Yours is going to leave a bit sweeter liquid because of the decent amount of leftover sugar. Use this to calculate your actual attenuation. Note this is done after your beer is FULLY fermented out.
[(OG-FG)/(OG-1)] x 100
Hope this helps!