The short answer is, it depends...
This is a simple question to ask, but not at all simple to answer. Migration between any two software solutions can become complicated quite quickly. The exact "how" of how you do this will generally vary a great deal from site to site.
Please Note: The word "content" here is being used to describe anything on the site that isn't part of your product catalog, shopping cart, and checkout.
For all use cases
No matter which use case you fall under below, your migration will need to include updating the site theme, site structure (information architecture), and more. If you find that doing this yourself is a bit too much, you can always work with one of our partners to have it done for you quickly.
I have an existing site, and it's content only
If your site only contains content and you haven't yet built an online store, then you would basically be able to begin editing your store and content on your site, and copy/paste most of your content. There may be some content that you have which may require adding a custom or third party extension to make it easier too.
I have an existing site, but it's a store only
Depending on how complex your product catalog is, you might be able to import your catalog using our import feature. Any remaining work would primarily be in duplicating your configuration for any promotions, taxes, zones, and shipping.
I have an existing site, it's store and content
This is probably the most complex scenario, which is almost certain to require the assistance of your technical team and/or our partners. You'll have a mix of imports using built-in features, data transfer, copy/paste, and more.
Migration Methods Available
No matter which bucket you find yourself in, you'll find that importing or migrating your current site has a path. You can move/copy files, copy/paste content, perform data imports, use one-time or recurring API connections, and more. We don't limit your ability to come aboard.