Summarize:

It should be a partially shaded corner of your yard. Ponds need some direct sunlight to be a healthy environment. However, frogs prefer shaded environments for breeding and shelter from the sun. Frog ponds can be as wide as you want, but they should be no more than a foot (or about 30 cm) deep. Be sure that your hole has shallow edges in it so that the frogs can enter and leave easily. Remove any roots, sticks, or stones that could damage the liner.  Frogs thrive best in shallow, non-moving water and are surprisingly susceptible to drowning in deeper water. If you don't have tapering edges to your pool, you'll need to provide some sort of incline. Frogs need a gently sloping exit, like a slab of rock, so they can easily get out of the water.  If you would like your pond to be a specific shape, mark out the edges with a piece of rope before digging. If you're digging up your lawn, keep the pieces of turf to help you secure the pond's edges. To keep the water in, you'll need a rubber or plastic pond liner. To protect the liner in the long-term, it's also a good idea to first insert a protective underlay between the plastic and the dirt to cushion the liner.  The easiest way to line your pond is to purchase a flexible or rigid plastic pond liner. However, any thick, durable plastic sheeting will do. Make sure that your liner is big enough to cover the entirety of your pond with a least two feet (about 60 cm) of excess on all sides. Ponds can also be lined with concrete, but you will need to treat it to ensure that lime does not leach into the water. Weigh down the plastic sheet around the edges of your pond with closely-packed rocks, and/or ring it with the pieces of turf you kept from digging the hole where your pond would go. Either way, make sure your perimeter is heavy and big enough to keep the liner in place. Once you've secured the pond's perimeter, you can cut away any excess liner. Ideally, you should let your pond fill with rainwater rather than filling it from the hose or tap. You can speed up that process by collecting rain in buckets to add to the pond. If you mix in a bucket-full of water taken from a local marsh or pond, it will introduce millions of microscopic organisms that can jump-start your pond's ecosystem. They will infuse the water with oxygen, making it more livable and appealing to native frogs in your area. You can also try planting a few native water plants in your pond to attract local frogs. Just make sure that the plants don't overtake the whole pond and choke other wildlife out. At least one edge of the pond should be thickly vegetated with leafy plants that grow well in your area. Plant grasses and leafy perennials around the edges of the pond to provide frogs with adequate shade, dampness, and protection. If you are looking to attract local species, it's a good idea to stick to native plants when planting around your pond. Pick a selection of native grasses, clumping plants (like ferns and lilies), and ground cover (like shrubs and vines) to grow around your frog pond. Keep in mind that it may take a couple years for frogs to populate your garden, even after you have created a suitable environment for them. If attracting frogs takes longer than you would like, you can try seeding your pond with tadpoles in the spring. Make sure you use a type of tadpole that is native to your area.
Choose a good spot. Dig a shallow hole. Line the hole. Secure the pond's perimeter. Let the pond fill with water. Add a bucket of natural pond water. Give frogs cover. Wait for frogs to colonize your yard or garden.