Sketch uses the native font rendering of macOS and because of that, text looks excellent. The benefit of native font rendering is that when you’re creating 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 typeface, size, color, etc.
You can add text by choosing the Text tool from the Insert pop-up menu in the toolbar (or press T). The pointer changes to the Text Input tool icon and then you can click anywhere in the Canvas to insert your text layer at that point. A new text layer will be inserted with “Type something” already selected, ready to replace.
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 create a new line, as opposed to a normal text box which increases its width to fit the content.
Sketch has support for displaying Rich Text pasted in from other applications. For example, if you selected some text from a website in Safari and copied it, in Sketch choose Edit › Paste with Style from the menu (or press Option-Shift-Command-V). The new, pasted text layer will contain the word(s) in the font, size, and color that it had been set in.
When you resize a text box in the Canvas its text size will not change. To change the text size, you must edit the text size value in the Inspector.