Entering the ∑ symbol in TeXstudio can be achieved by using LaTeX's mathematical mode command. The specific steps are as follows:

1. Select the position where you want to insert the ∑ symbol in the editor.

2. Enter the mathematical mode in one of the following ways:

-use the shortcut key "ctrl+m".

-Click the Math Mode button on the toolbar.

-select "mathematics"-> "inline mathematics" (inline mathematics mode) or "display mathematics" (independent mathematics mode) in the menu bar.

3. In the mathematical mode, enter the `\\ sum ` command to insert the ∑ symbol.

4. Press the Enter key, and TeXstudio will automatically convert the command into a ∑ symbol.

Explanation: TeXstudio is an editor specially used to edit and compile LaTeX documents. The ∑ symbol is one of the mathematical symbols in LaTeX, which stands for summation operation. In TeXstudio, you can insert the ∑ symbol by inputting the `\ \ \sum command. TeXstudio provides the support of mathematical mode, which is convenient for users to input and edit mathematical formulas.

Extended content: Besides the ∑ symbol, LaTeX also provides many other mathematical symbols and commands, which can be used to represent various mathematical operations, relationships, symbols and so on. For example,' \int' stands for integer symbol,' \sqrt' stands for square root symbol,' \frac' stands for fraction, etc. Mastering these mathematical symbols and commands can help users edit mathematical formulas and expressions better. At the same time, TeXstudio also provides real-time preview, automatic completion and other functions, which makes editing and typesetting mathematical documents more convenient and efficient.