Once you are logged in to your Markate account,
Step 1: Hover over Sales and click Estimates.
Step 2: Click +New Estimate.
Step 3: On the New Estimate pop up, click Standard Estimate.
Step 4: On Submit Standard Estimate page, fill in all details like Customer, Job location and so on along with item lines.
Step 5: Now, click Set Markup.
Step 6: On the Set Markup pop up, either you can enter Markup value in % or $. Suppose you enter 5%, then your customer will see item price + 5% of the item price on the estimate and if you enter $5 then he will see item price + $5
Step 7: Click Set Markup and Markup value is added to your Estimate,
Step 8: Click Save as Draft or Preview to Save the Estimate
And this is how the Markup is merged to the item price and the customer will see this way,