The idea of a period of tribulation preceeding is based upon a section of the Olivet Prophecy, which reads as follows:
For then there will be great tribulation, such as has not been from the beginning of the world until now, no, and never will be. And if those days had not been cut short, no human being would be saved. But for the sake of the elect those days will be cut short (Matt 24:21-22; cf. Mark 13:19-20; Luke 21:22-23)
The context is a great siege against Jerusalem. In all three accounts, the prophecy moves on to speak about the second coming of Jesus Christ. Interpreters disagree about whether the siege of Jerusalem refers only to AD 70, when the Romans destroyed Jerusalem, or whether there is a future fulfillment. If the latter interpretation is correct then we should expect a period of tribulation connected to a siege of Jerusalem prior to return of Christ. The prophecy does not disclose whether this tribulation effects the whole earth, or just Jerusalem and the surrounding area (as in AD 70).
The Book of Daniel also seems to refer to period of tribulation prior to the resurrection of the dead, which we know from elsewhere in scripture will occur at the return of Christ (Dan 12:1-3). This does seem connected to an invasion of region of Palestine (cf. Dan 11:40-45). The phrase “your people shall be delivered” seems to indicate that the Jewish people will be saved from the invader.
The other significant reference to a period of tribulation is in Revelation 7, where we are presented with two groups of people. First, a group of 144,000 “from every tribe of the sons of Israel” are “sealed” (v4), seemingly before some “harm” strikes the world (v3). The second group is a multitude “that no one could number from every nation” (v9). These are described as “coming out of the great tribulation” (v14). Revelation is highly symbolic and notoriously difficult to interpret. One way of interpreting these verses is to see the first group as those who will be specially protected from the coming tribulation (cf. Rev 9:4), and the second group who have endured the tribulation and have come into God’s Kingdom. If we interpret the 144,000 literally, this would imply a relatively small group of Jewish people will be protected from tribulation. However, elsewhere the 144,000 are characterised as those “who follow the Lamb wherever he goes” (Rev 14:4), perhaps indicating that spiritual Israel is intended.
So to answer the question specifically, we do not know the extent of tribulation, who will be involved, or who will receive special protection.