Here you go
col-lg-2 : if the screen is large (lg) then this component will take space of 2 elements considering entire row can fit 12 elements ( so you will see that on large screen this component takes 16% space of a row)
col-lg-6 : if the screen is large (lg) then this component will take space of 6 elements considering entire row can fit 12 elements -- when applied you will see that the component has taken half the available space in the row.
Above rule is only applied when the screen is large. when the screen is small this rule is discarded and only one component per row is shown.
Below image shows various screen size widths :