There are books, on line tutorials, everything. In the most simplistic terms, most Sports can be bet with a Points, Goals, etc. line where you can take either side OR a Money Line, where you simply pick the winner. But, option 2 weights the line, heavily against you for the team most likely to win and heavily for you for the underdog.
There are many, many, many additional permutations and combinations based on the Total Score over multiple time periods and the same bet described above, over multiple time periods. ( Think 1st. Quarter)