The grocery store Aldi is not a membership store like Costco or Sams Club so you do not need a membership to go into or shop in Aldi stores.
I do most of my grocery shopping at Aldi and actually find Aldi cheaper for groceries than Costco, Sams Club or even Walmart.
Still sometimes Walmart is cheaper on a few types of groceries but Aldi is where I do most of my shopping to save money on groceries.
All you do is go get a shopping cart after putting in a refundable quarter that you get back when you lock the shopping cart back up and then go shopping for your groceries inside Aldi.