Sketch uses the native font rendering of the operating system and because of that, text looks excellent. The benefit of native font rendering is that when you’re doing a website design you’re sure that text looks accurate. Sketch also supports text styles so you can have multiple text layers share the same font, size, kerning etc.
You can add text by clicking the text icon in the toolbar. The cursor changes to a text cursor and then you can click anywhere in the canvas to insert your text layer at that point. You will see text being added and selected so you can start typing immediately.
You can also click and drag to create a text box of a fixed size. When the text gets too big to fit inside the box, it will resize downwards, as opposed to a normal text box which increases its width to fit the content.
When you resize a text box in the canvas its text size will not change, except when you resize auto-width text using the resizing handle at the bottom.