Monday is the first day of the week, and is usually the first day of the working week too. The next day of the week is Tuesday.
Tuesday is the second day of the week. The day before Tuesday is Monday and the day after Tuesday is Wednesday.
Wednesday is the third day of the week. The day before Wednesday is Tuesday and the day after Wednesday is Thursday.
Thursday is the fourth day of the week. The day before Thursday is Wednesday and the day after Thursday is Friday.
Friday is the fifth day of the week. For most people, it is the last day of the working week. The day before Friday is Thursday and the day after Friday is Saturday.
Saturday is the sixth day of the week and the first day of the weekend. The day before Saturday is Friday and the day after Saturday is Sunday.