Maghrib tonight (Tuesday the 7th) marks the beginning of the last 10 nights of Ramadan.
Ramadan is informally separated into three 10-night periods. The first 10 nights are known as the nights of Mercy; the second 10 are the nights of Forgiveness; and the last 10 are of Salvation. And one of the upcoming nights—probably an odd-numbered night, so tonight, Thursday night, Saturday, Monday, or Wednesday, unless we started on the wrong day, in which case it could be yesterday, Wednesday, Friday, Sunday, or Tuesday nights—is Laylatul Qadr: the Night of Power, the night that is better than 1000 months when Allah azza wa jall sends down His decree for the coming year.
For these last 10 nights, Muslims strive to worship even more than we have throughout the previous 20 nights, and if we’ve been slacking off during the middle, as so often happens, we’re urged to pick it up and finish strong. The Prophet, peace be upon him, used to spend the last 10 nights and days in the mosque, worshiping more or less constantly, and leaving almost all worldly tasks. Some brothers and sisters engage in Itikaf and book space in the mosque, where they stay from Maghrib on the 21st night until sunset on the 30th night (or the 29th, if the new moon is sighted, thus ending the month of Ramadan and beginning the month of Shawwal).
Don’t let the calculations distract you: they’re not important.
What is important is worshiping God with the best of your ability all of the time, trying to constantly get closer to God, and occasionally—like the last 10 nights of Ramadan—trying to pick it up even more.