If you just want to centre-align the text itself, add style="text-align: center;" to your HTML element that holds the text (<div>, <p>, etc.)
If you want to centre an element horizontally on the page, like a <div>, you can do so by setting a width that's less than 100% of its parent container and then adding style="margin: 0 auto;".
Those are the two easiest solutions to the most common use cases. There are a lot of different ways to position things on the page, but since you're just starting out you probably don't want to get into flex or grid yet.