OK, I'll take the OP as stated.
There are two main types of support and resistance levels.
1.Price
A support level is where the majority of market partipants take the (recurring) view that price (after falling) is too low. This buy pressure pushes price upwards.
A resistance level is where the majority of market partipants take the (recurring) view that price (after rising) is too high. This sell pressure pushes price downwards.
Often these price levels will flip between support and resistance. This is known as a Support/Resistance Pivot
These levels can be horizontal or diagonal (ie a trendline).
2.Mathematically derived price levels
This includes Floor Pivots, Fibonacci Floor Pivots, Fibonacci Retracements/Expansions, GANN, Market Profile etc. There are several websites that will give you these values.
Trading is all about (repetitive) pattern recognition.
HTH