If you've been using EF 6 until now, you should take the time to learn about what has changed in EF Core. The basic concepts and usage of EF should be familiar, but there are some new additions (and some removals), which will affect your learning curve for picking up EF Core.
If you have been doing Code First development, you should already be familiar with building your own models in your application code. If you have already used Migrations, you should also be familiar with generating/updating your database by triggering a migration. However, if you have gotten used to visual data modeling tools and EDMX files, you may have to unlearn a few things. EDMX files are Entity Data Model files that can be used to represent your data model visually, using earlier versions of EF.