Four operations are simple and basic mathematical operations, that is, four operations of addition, subtraction, multiplication and division. Four operations are the important content of primary school mathematics and the basis of learning other related knowledge. These four operations are considered as basic mathematical operations and are often used to solve various mathematical problems and calculations.

1. Addition: Addition is the operation of adding two or more values to get a sum. For example, 1+2 = 3, 3+4+5 = 12.

2. subtraction: subtraction is the operation of subtracting one value from another to get the difference. For example, 5-3 = 2, 10-4-2 = 4.

3. Multiplication: Multiplication is the operation of multiplying two or more numerical values to obtain a product. For example, 2 × 3 = 6, 4 × 5 × 2 = 40.

4. Division: Division is the operation of dividing one value by another to get the quotient. For example10 ÷ 2 = 5,20 ÷ 4 ÷ 2 = 2.5.

The four operations are that when the first-level operation (addition and subtraction) and the second-level operation (multiplication and division) appear in the same formula at the same time, their operation order is multiplication and division first, then addition and subtraction. If there are parentheses, count the parentheses first, then count the parentheses. The operation order of the same level is from left to right.

Four operations are the most basic and commonly used operations in mathematics, which are widely used in daily life and various disciplines. They provide a foundation for mathematical reasoning and problem solving, and play an important role in computer science, physics, engineering and other fields.