SELF SWITCH AND VARIABLE[RMXP]

hi everyone,long time no see i have some question about my new RM(i use xp now before i have 2003 and i'm also very sad because i can continue my project in rmxp)it about Self Switches can you use the same switch in same map.EX:
i use my Self Switch A on my treasure chest1 after that i make a new treasure chest2 with self switch A in the same map or i must use the self switch A in other map after i make a Treasure chest1 with self switch A.
Variable i know how to use that but i have no idea what variable use for can you give an example what event use variable(i've already seen an example like making minigame but i want other example)

Sorry for asking you so much and i'm sorry if there is a mistake in my English i hope you understand what i mean :D