Itemized deductions are deductions you can enter like mortgage interest, property taxes, medical expenses, charitable donations, etc. There are some people who have enough of those deductions to exceed their standard deduction, so they enter those deductions instead of taking the standard deduction. The standard deduction is money you do not pay tax on. The itemized deductions are also income that no tax is owed on, so they can increase your refund, or lower the amount of tax owed.
If you are single and have an income lower than 12,200, then you have no need to itemize your deductions.