The formula bar appears when you open the Excel. However, if the formula bar disappears and you want it back, please follow the steps below:
Step 1: Click the "File" Tab from the ribbon;
Step 2: Click "Options" from the left navigation menu;
Step 3: Click "Advanced" from the left navigation menu in the dialog box;
Step 4: Check "Show formula bar" under the "Display" section;
Step 5: Click "OK" at the bottom.