Choose your images, drag them into the order you want, and export them as a single PDF — one image per page. JPG and PNG both work, and you can mix them in the same document.
The conversion runs entirely in your browser. Your images are never sent to a server, which matters more here than it does for most tools: the things people convert to PDF are usually scanned documents, ID photographs, receipts and contracts. None of that leaves your device, and there is nothing on our side to leak.
A note on size: a PDF built from photographs inherits their resolution, so a dozen phone pictures can produce a file of several megabytes. If you are attaching the result to an email, resize the images before converting rather than after — a PDF cannot be made smaller without re-encoding what is already inside it.