split() function splits the string by the character you choose, here “comma” (,) producing an array of the parts that were separated by that charachter
You reference the parts by index starting from 0 onwards.
Thus, the string “7pm this evening,11am tomorrow” when split by comma becomes an array (list) of two items (as there is only one comma). The first item referenced as [0] (meaning at the first position) becomes “7pm this evening” and the 2nd part referenced by [1] (meaning at the 2nd position) becomes “11am tomorrow”.