To get started use Quick Start guide.
If you've already been using Bootstrap 4, there are a couple adjustments you may need to make to your project:
Bootstrap Vue is to be used with Bootstrap 4 CSS. Please see Browsers and devices for more information about currently supported browsers by bootstrap 4.
BootstrapVue is written in Vue! So this is up to your project and bundler that which browsers are supported. If you want support older IE, Android and IOS devices, you may want using Babel Polyfill