The first step is gathering up the stuff you need,mainly organic soil, I use miracle grow organic gardening soil, it's about 5 dollars a bag, and of course you will need to decide on what to use as a cap to hold down the soil. You can use playsand/poolfilter sand, or quickcrete has a sand that is pretty course, you will need to wash it to get the fine silt out or spend a few hours filling and draining the tank. (to wash it you basically put it in a bucket put a hose down in the bottom of the sand turn it on and let it run till the water comes out clear, the playsand or poolfilter sand you won't need too.
When you got those things ready you still need to plan out the layout of the tank, decide on a center piece and what type(s) of hardscapes you will use like rocks/driftwood/ornaments and the like.when doing the soil you need to keep in mind that you want it to slope up towards the back of the tank and have a flatspot in the front and center.
You really can't see so well in the pic but the soil is slightly higher in the back and around the edges the soil should be around 2 inches in the thinnest areas and go to up to 3 in the thicker areas, you don't need to break out a ruler it does not need to be precise. you should lightly pack it down, the miracle grow soil is full of organic stuff that will decompose and feed the plants.
This is a step I add, in a betta tank it is not really required, This tank will not be for bettas, it will have a variety of fish and some are known for digging to prevent this I use craft cloth, the stuff we all use for our DIY tank dividers.
I put a thin thin layer of the playsand over the craft cloth to act as a filter to keep the soil down where I want it to stay it is maybe 1/8 or 1/4 inch thick or so again you do not need to be precise.
Now it's time to add the gravel you just put about an inch or so or gravel in this gravel seems to be giving the illusion of being thinner than it is but you just maintain the slope of the soil/sand and you are good to go.
Water added notice it's crystal clear I put in a plant and some of my hardscape used filter media out of other tanks did my water conditioner to get this tanks cycle started Will add plants and the rest of hard scape in about a week as well as the fish that will call this 46 gal bowfront home will add pics of that process........if it wasn't for the tiny bubbles on the glass you would think it was empty. It took us about 35 minutes or so to get this done.