During the process of placing an order on your site, for your customers, and them actually receiving their product, they will be sent some automated emails with information about their orders. These are done automatically, so you don't need to worry about manually sending them for each order.
You will definitely want to customize the notification emails with your store's logo and colour scheme. To do this:
Sign into your Shopify Admin > Settings > Notifications > Click the "Customize" button on the left-hand side.
From here, on the right-hand side of the page, there will be some options for you to upload a logo to replace the plain-text store name, and also an option to set the accent colours for the buttons and links.
Upload your logo, and set the size (I recommend making it at least 200 pixels). For the accent colour, I recommend using the same colours that you're using for the website's buttons, to maintain a uniform look. Save changes when you're happy with how it looks. It will apply these changes to all templates, so you only need to set them once. Here's how mine looks:
On the page where you clicked the "Customize" button, it does give you the option to edit each of the notifications individually, but this requires some extensive custom coding knowledge, in order to not break anything. I recommend leaving these how they are, or else reaching out to a Shopify Design Expert if you absolutely need them changed.
Need more help with this step? Check out Shopify's help docs for notification settings by clicking here.