Please explain step by step how to find MSE and Weighted moving average forecast in EXCEL!!

$12$

$20$

$\backslash$table$[[$Week$,\backslash$table$[[$Time Series$],[$Value$]],\backslash$table$[[$Weighted Moving$],[$Average Forecast$]]],[1,17,],[2,21,],[3,19,],[4,23,19\mathrm{.}33],[5,18,21\mathrm{.}33],[6,16,19\mathrm{.}83],[7,18,$