I have read that there are not scenes in Adobe Edge Animate, and symbols can replace them. So I made a symbol called "mission1" and in the main scene is a button, whose should make main scene disappear and start playing mission1's timeline (just like feeling of motion between two scenes). How to get that?
Please read my blog here about symbol scope:
All this depends on how you want to handle things.
You could have your elements on the main timeline disappear by changing the opacity from 100 to 0 then turning display off to reveal your mission1 symbol and play that symbol when the timeline is at that place where you want to show and play your symbol.
Of course you could also load your symbol dynamically with a trigger on your button with sym.createChildSymbol('librarySymbol', 'StageorContainer');
Note that the symbol will load on the stage at top=0, left=0. If you need to move it you will have to use CSS.
If you use a container, your symbol will load into the container at top =0 and left =0. If you need to move it, there also you need to use CSS.
If you are going to use several symbols you can either load them and remove them dynamically or place them on the stage and set labels where visibillity is turned on and off then go to these labels and place the symbols there. There is also the possibility to use scrolling to show different areas of the timeline. etc.
Everyone is different and does things their own way.