Lay Out Your Walkway
The first step in installing a walkway is planning its path. You'll want to mark the walkway with stakes and a string (if it's a straight path). Consider its design and use as well. Also, decide if this will be a heavily-trafficked walkway, where it will need to be wide enough for two people, or if this will be a secret garden pathway, where only one person needs to walk on it. Consider drainage as well, so slope your rocks away from the house. Ensure you don't choose slippery stones.
Dig Out the Walkway
You'll want to make the walkway as flat as possible, so you'll have to remove all of the ground cover material, such as the grass. Be sure you get the roots as well. Ideally, you'll want to excavate about five inches so the flagstones will be even with the surrounding ground. Make sure you compact the soil when finished. If you set your walkway higher, it will be drier overall than the surrounding ground.
If you are using edging, you'll install that next. Edging can be all different types, including metal, brick, or even wood. Edging can give your walkway a nice, finished look, or you can simply use the ground around to hold your flagstones in place.
Install Landscaping Fabric
Landscaping fabric will help to ensure weeds don't grow underneath your flagstone walkway, and it allows the soil to still breathe. Try to use pieces that are as long as possible, as the more you cut it, the more opportunity there is for plant growth.
Add an Underlayer Material
You'll want to put a supportive underlayer material. Many people choose gravel and sand, but sand is the minimum recommended to install your flagstones on top of. This adds in support so when you walk on your walkway, it doesn't move when your flagstones settle in. Gravel also helps your walkway to drain better so water does not pool. You'll want to make this layer level and compact. You can use water to help with compressing the material.
Lay & Install Your Flagstones
This is the fun part. Now you get to design your walkway with the stones you have chosen. You'll want to leave small gaps in-between, or wider gaps if you plan to plant in-between the walkway. The most important thing here to keep in mind is to ensure your stones are level with one another. You can add or remove sand as you go along to adjust for this. Here's where you can choose the look, and by alternating unique colors and sizes, you'll add character to your flagstone walkway.
Fill In the Gaps
Finally, you'll want to use sand or stone to fill in the gaps. This will stabilize your walkway and prevent it from moving. You can spray the walkway afterward with water to help your material settle and then add more if needed. If you're planting the walkway, here's where you will add in potting soil and then your plants last.