How make a simple start menu with button “Start” after pressing which you go to the main level?
P.S. My skills very low, please, more detailed.
Download the content examples from the market.
There is a HUD example, it has buttons that does stuff 
I still don’t get it.
Show us what you have so far.
I apologize for not going into very much detail but how I solved it as an easy solution was to first make sure I could draw textures and hitboxes on desired locations on the screen as this will be used as the menu (via the HUD blueprint)
Then I made an event recieve hit box click connected to a switch on name (hitboxes will have to be set to proper names) and if quit is pressed then is simply quits the game.
To remove the player controls while this happens I disable mouse and events for the player controller until “start game” is pressed which in turn opens a gate to give control back to player and another gate to disable the Menu parts in the HUD