Does the amount that is taken out for taxes fluctuate or change every year? Or does it depend on a person's job and other variables?
If you mean the amount that is taken out of your paycheck for taxes,then yes the amount depends on certain variables. The biggest variable that you can't control are the withholding tables employers use to calculate how much tax to withhold. This year the withholding tables underwent a major change due to the new tax reform. Likely, you are having less withheld from each paycheck now than you had withheld in January.
You do have some control over how much is withheld for federal tax withholding and state tax withholding. The social security and medicare amounts are set and cannot be changed. To change your withholding you need to complete a new withholding certificate and give it to your employer. The more allowances you claim on line 5 the less tax will be withheld. You can print the federal withholding certificate here: https://www.irs.gov/pub/irs-pdf/fw4.pdf