Create two buttons and put "save" and "load" in their corresponding name and text. Add an event, choose the button "save", select the option "on clicked" and in the add action, choose system and there you should find another option saying "save". To end, put the slot name with which you will save your game. To load this, do the same process but in the load button and choose the option load, put again the slot name that you had put in the previous step.
I've tried this and it worked for me!
Hope it works and sorry for my english!