Use the search bar to find and select the relevant Object (e.g. Account, Contact, Custom Object)

In the left panel, click Page Layouts

Select the layout you want to update (e.g. Account Layout), and click Edit

From the top palette, click Fields

Find the field you want to add

Drag and drop the field into the desired section on the layout, then click Save
👉 Tip: You can place it in an existing section or create a new section

Go to a record of that object (e.g. Client Account)

Confirm the new field appears on the page