My .sc file for ma model looks that:
Spacecraft "Stacja kosmiczna 1"
ParentBody "10 Leonis Minoris 7"
TidalLocked true // up vector automatically derived from FixedPos coordinates
Obliquity -1.7 // tilt angle adjustment (degrees)
EqAscendNode 1.18 // tilt angle adjustment (degrees)
RotationOffset 190 // orientation azimuth (degrees)
FixedPosPolar (119.3385 -7.1039 4676.765) // longitude, latitude and distance from the parent planet center
So, my model "Stacja kosmiczna 1" should appear on planet "10 Leonis Minoris 7". It does't. Why? Sc file should be in same place as .sss file?
10 Leonis Minoris 7 is a procedural (random) planet, automatically generated by SpaceEngine. At the moment we can't use a procedural object as ParentBody (and technically the reference should use the abbreviated name for the constellation like in search window, "10 LMi 7"). So you could place your model on another existing catalog planet, or export 10 LMi 7 script and make it a catalog entry.
The long and lat I read from left top corner on screen there are data about planet and position of camera? Where I can find "distance from the parent planet center" to put my 3d model?
Yes, lon and lat are longitude and latitude of the location in the center of your camera view, the distance from the parent planet center is the planet radius plus the "distance" value of the camera or "Landscape height" if you want the object right on the surface. Manual adjustments may be necessary
When I create a .sc file for my model and enter a specific location, my model should always appear in that particular place, right? No matter where I am at the moment, when I press "create" the model will appear where I described it in the file?
When you make a .sc file for that specific location, your model will be automatically loaded once you start SpaceEngine, but it's a single static object and you can't interact with it (if it's a spaceship you can't pilot it). When you create another model from the spacecraft manager you'll have a copy, unrelated to that script file.
If you want multiple objects, you'll have to specify a location for each one of them in that script. For buildings, you'll have to place multiple objects with a different name like "Building01", "Building02" etc, just as in ApolloLandingSites.sc. This if you want to place them in locations far from each other. For small buildings nearby you can place multiple copies of those models in your .sss file and adjust their position with the in-game editor.
Depending on how you organized your folders in addons, you could need to change the folder path of your model, SE could search in another place.
See if you find error warnings in your se.log or in the console ( ~ key).