Enter three "-"symbols in succession, then press enter and insert a thin line;

Method 2:

Hold down the Shift key, input three "-"symbols in succession, then press enter and insert a thick line;

Method 3:

Enter three "=" symbols in succession, then press enter and insert a double line;

Method 4:

Enter three "~" symbols in succession, then press Enter and insert a wavy line.

The effect is as shown in the figure: