It is really quite easy.
You pick out the set(s) you want. Carry them to the checkout queue and pay for them.
Apparently, some people feel shame or embarassment when buying things at the store. Why? Are the people at the store our judges? I think not. Buy what you want. As long as you pay for it, the workers at the store aren't going to care one bit what you're buying. Honest. I used to work in retail, and after a bit, you just want the people to buy their things and get the hell out.
There can be no shame when buying Lego. It's the perfect toy. Lego Zen shall soon follow.