The short version is that Patternism is a combined pattern viewer and row counter for knitting and other stitch-work projects. You start by finding a PDF of a pattern with Safari, or any other app, and opening it up in Patternism. Once there, you can not only use the row counting features, but you can add per-step annotations. You can both add highlighted areas to the pattern and write down notes. Both are tied to the row number, so if you're using a pattern that repeats, or if you knit something a second time, you'll see all your previous marks at the right time.
The easiest way to add a pattern to Patternism is through Safari. Browse to the PDF you want to add, then tap the screen. You should see the "Open In" menu appear at the top. Tap it, then select Patternism. Once you do, the PDF will be saved locally and you can get started. This also works from any other app that supports the iOS "Open In" menu, such as Mail or Drop Box. If you don't see Patternism in that list, try scrolling it. If it's still not there, you may be at the limit for PDF opening apps.
The other way to get a PDF into Patternism is through iTunes File Sharing. This is a good way to go if you have a lot of PDFs on your computer or if you have a lot of PDF viewers on your iPad, and Patternism doesn't make it into the "Open In" menu. To add a file this way, click on your iPad under "Devices" in iTunes. Go to the "Apps" tab, then find Patternism in the list at the bottom. Add your PDFs there and sync your iPad. The files will show up in Patternism next time you launch it.
Tip: The iTunes window above can also be used to get files back out of Patternism. If you want to back things up, or just use a pattern in a different way, just find your pattern in the list and use the "Save As" button to copy it to your computer.
Patternism gives you four stitch counters to work with. Each counter has a big, numbered button, to increase the count, and a separate "Reset" button to change it back to zero. The "Row" counter has a "Frog" button instead of "Reset", which will roll back a single row. The two unlabeled counters are independent and can be used for any purpose. To assign a label to them, open up the project settings with the "Edit" button at the top of the screen. From there, you can also choose to have either of the two extra counters work backwards by flipping the "Reverse" switches.
The "Row" and "Repeat" counters are also linked. Increasing the repeat count will reset the row count, and frogging when your row counter is zero will reduce the repeat count in addition to setting the row to the previous value. If you've selected the option, you can also choose to have the repeat increase automatically after a certain number of rows.
The three "Reset" buttons all have a limited undo feature. When you use one of the buttons, it will temporarily turn into an "Undo" button. If you click it, it will restore the counter you reset to its previous number. It will stay as an undo button until you change any of the counters.
Notes and Highlighting
Hitting the "Add Highlight" button at the top of the page will drop in a new highlighted area on the page. You can drag it around the page, or resize it by dragging on the white squares around its edges. You can add as many highlights to the page as you need. If you need to move, resize, or delete one you've already placed, tap it once to activate it.
All of the highlights you place, as well as the part of the PDF you're viewing, are tied to the "Row" counter. If you start a new repeat, or if you frog backwards, Patternism will automatically redisplay the highlights as you had them set when you finished that row.
If you hit the up arrow in the bottom-right of the pattern area, the row information area will appear. From here, you can change the highlight color and, more importantly, you can add notes about the current row. To add notes, just tap the text area. Just like highlights, the row notes will pop up automatically on future repeats.
There are two global settings you can change for Patternism, from the main iPad "Settings" area. The first is an option to start counting at 1, instead of the default 0. This allows you to easily keep track of which row you're on, instead of how many rows you've completed. The other setting lets you keep the iPad from going to sleep while you're working on a row.
If you find yourself needing to just reset a project, choose the "Reset project data" option to delete all of the highlight and note information you've saved. To go further, you can delete entire projects by opening the project list, then swiping across its title.