Both manual and power lawn edgers create neat, even cuts. Manual lawn edgers typically have a rolling, sharp-edged cutter affixed to some type of stick. Power lawn edgers run on either gas or electricity. If you have a lot of area to edge, a power lawn edger will probably suit your needs better than a manual one.
Shovels are best for edging large swaths of land without a mechanical lawn edger. Any type of shovel will do, but a flat-headed shovel works best for edging. Flat-headed shovels hit the ground evenly, meaning the shovel is working with you instead of against you.
A hand trowel is like a small shovel. It is hand-held and convenient for edging small sections of land, such as around a small flower bed. You can also use a trowel to dig small trenches. If you have a decent amount of earth to tend, don't rely on a trowel. It takes a lot of time and effort and will probably result in some sore hand muscles before too long.
Digging a trench in your yard won't be necessary often. A trench is typically defined as a deep, narrow hole in the ground. You may want to dig a trench for irrigation or landscaping purposes, such as around a garden.
Shovels are the best tool for digging a trench without resorting to heavy machinery. A flat-headed shovel works well for leveling the ground. An entrenchment shovel is a small, fold-up shovel that is typically used to dig trenches during wartime but can also be used in the yard.