That's it. Then we continue in the same spirit: we laid out the cement, installed/leveled a piece of the curb. We coat the joints of two curb fragments with a layer of cement. We remove its remains immediately after installation and leveling. If it dries, there will be unsightly marks that are not easy to get rid of. If installing one curb takes a little time, you can lay the solution on several "curbs" at once. It will be faster.
The most questions are usually about crushed stone. Not lithuania mobile database lays it. You can do without crushed stone if the soil is sandy. Then just level the bottom of the trench and you can continue working. But if the soil is clay or loam, black soil, then without gravel backfill in the spring, the curbs will simply be squeezed out in different directions. So here gravel increases durability. Can I use gravel or construction waste instead of crushed stone? It is better than nothing, but not the best option. Especially broken brick. Over time, it will collapse and turn into crumbs, the curbs will sag. So, it is better not to, and then - see for yourself.
We select the size of the curbs (height) taking into account that part of it needs to be buried
One more thing. Clay, black soil and loams "eat" gravel incredibly quickly. It sinks into them. If you want a "long-lasting" path, lay geotextile on the bottom of the trench. Its edges should go beyond the trench. Just straighten them along the edges. When you install the curb on cement, wrap the edges of the geotextile and cover the concrete with film. After a week, you can remove the film and fill the trench with earth. You don't have to unroll the edges of the geotextile. Then the crushed stone will not wash away.
A few words about how much solution to mix. It depends on how fast you work. If you have little experience with such work, it is better to mix very small the first time - for two or three stones. The thing is that if the concrete starts to set, you will have to throw it away. It will not recover if you add water. No, you may get the desired consistency. But the concrete itself will be nowhere. It may not gain strength at all or be very crumbly. In some cases, so much so that you can just pick it out with your finger.