Just grab as needed. I usually look for the ones that aren't filled with poop - you'll see the black line running down their bodies. I rinse and pat dry and even dust to improve grip. I'll chill them (fridge/freezer) as anesthesia so they don't fight back so viciously when being eaten or cut up.

Eventually, the constant layering of food and bedding will fill your bin with "black gold" = poo. I scoop 3/4 of the worms and poo into a big colander, put down bedding and food in the bin, place the colander in the bin on top of the food, replace bin lid. Most of the worms will crawl out of the colander leaving the poo for you to use in your garden.

When you first get your worms, put them in the bin with food and bedding and leave the lid off for a day or two until they settle in. Some people advocate leaving a light on during that time since the worms are light sensitive. I never do cuz the air in my house is so dry, the worms can feel it.