You can insert a text box in Google Docs by following these steps:
Open your document in Google Docs.
Place your cursor where you want to insert the text box.
Go to the "Insert" menu and select "Drawing." This will open the Google Drawings editor.
In the Google Drawings editor, go to the "Insert" menu and select "Shape."
Choose the shape that you want to use as your text box. You can choose from several basic shapes like rectangle, circle, and arrow.
Click and drag to draw the shape on the canvas.
Next, go to the "Text Box" option in the "Shape" menu.
Click on the shape where you want to add text and start typing.
You can customize the text box by changing the font, size, color, and alignment of the text.
You can also customize the shape by changing its color, border, and other properties.
When you're done, click "Save and Close" to insert the text box in your document.
Your text box is now inserted in your Google Docs document. You can move and resize it as needed. Note that if you want to edit the text or shape of the text box, you can simply double-click on it to open it again in the Google Drawings editor.