[How to export a finished design to print?]

Hi, I'm new to the forum and have been searching in vain for the section where I can post questions involving Affinity Designer for Mac, instead of just for iPad. Since I have an iPad Pro, and there is going to be a version for it soon, I will pose the question here:

I love Affinity Designer, but have been unable to discover how to export a finished design to print out as A4 in high resolution. It always comes out pixelly, which is self-defeating unless I'm just making a blog. How can I make a vector illustration export in a non-jaggedy high-resolution format for the purposes of printing in a magazine or book? Any help would be much appreciated (including a clue as to how to post a question on Affinity Designer for MAC. Thanks, and my apologies if I overlooked something!