hi dark killer!
the objects are either models or entities, like the health cabinets which are entities and the tank which is a model, you get all these by right click on the grid, then there are all the misc_models you can choose
for terrain creation you should use easygen, there are some tutorials on it available but i don’t know if there’s an up to date one, at least mine is not quite up to date but you could read it as well for understanding the basics (www.wolfproject.net), there are many tutorial-links in the sticky readme-thread and already there are many terrain questions here so just read everything you can get…
leaks: you need a structural brush to seal your world from the void, a patch isn’t structural and detail patches don’t work either, terrain is by default detail so the engine doesn’t calculate it in vis-process, when you use terrain you always have to enclose it in a structural hull, making hulls though is not an easy task but i recommend to learn how to do it before you do too much work with your map or at least to learn the basics of vis…
perfect circle: it’s not possible to do a perfect circle it always has edges but the edges you see in radiant don’t appear in game, in game circles (cylinders) are rendered rounded - your circle road could get difficult to do though, you could try to make a cylinder and thicken it or cap it and then remove all unused patches and so on but it would be difficult to line up the sorrounding terrain/brushwork with the road as the edges wouldn’t meet any grid points, so probably it’s better to either do a texture for your ground that looks like you want it with the road and grass or whatever painted right or to do the patchwork yourself by hand and do it as round as possible (but yet not perfect)…
did that help?