Speaking from my own experience as a former born-again Christian....
Fundamentalists, evangelicals, Pentecostals, born-again Christians. It doesn’t matter what you call them or what they call themselves. The small differences in doctrine and practice are negligible. What ties all of these groups together under the blanket term “fundamentalist” is a belief in the “five fundamentals” of Christianity:
• Inerrancy of the Scriptures
• The virgin birth and the deity of Jesus
• The doctrine of substitutionary atonement through God's grace and human faith
• The bodily resurrection of Jesus
• The physical return of Jesus and the rapture
Sometimes the last point is replaced with "the miracles of Jesus.
Technically, fundamentalists are subset of evangelicals, as are Pentecostals. Fundamentalists are more focused on obeying the rules and law of the Bible, while Pentecostals are more concerned with spiritual experiences. There are so many sub-groups, that it's almost impossible to be detailed about anything. Fundamentalists are, as far as I have observed, are conservative and even reactionary in their politics. Evangelicals, as a larger group, may be conservative or liberal.
More recently, the term fundamentalist has come to refer to people of any religious belief who are dogmatic, legalistic, and literalist in their interpretation of the scripture of their religion, and who disregard any evidence or philosophy that is not in agreement with their holy book.