When you create your estimate, along the bottom there will be a Save and Send option. If your estimate is complete and has your customer's email address on it, you'll be able to send it to them for approval. Here's a video that outlines these steps: How to Send Estimates.
If you don't see that option, or have any questions, please feel free to reach back out to me here. I'll make sure you can get that estimate over to your customer. :)