Help - switching to illustrator - canvas size and image output size

You are welcome, maybe.

One of the crucial differences from what you are used to is that here you work with Artboards within a Workspace rather than a Canvas (the word Canvas has somehow found a mousehole into Illy terms and is sometimes used for either Artboard or Workspace to muddle things up completely): the Workspace is the total area where you can draw and do, and the Artboard is the area for printing/PDF creation and can be used as limiting area of what is exported; you can have multiple Artboards with their own internal measuring.

The suggestions of integer values can be used when you set up an Artboard, and when you place artwork; one of your friends is the Transform palette where you can use the Reference point at one of the corners.

Smart Guides are also your friends, especially because they can tell you when you are within snapping distance of whatever you wish to snap to in order to get accurate alignments; and then of course your Align palette.

These are only a few things to start reading up on. What was once known as (what you should Read) The Fine Manual is in the documentation, which you may find is overwhelmingly written for those with a (good deal of) knowledge, but a good Adobe source of general/specific information is formed by the helpx pages.

Here is a blank helpx search page (to Bookmark) where you can just start typing in:

https://helpx.adobe.com/search-results.html?q=&scope=%5B%22helpx%22%5D&subscope=%5B%5D&limit=10&start_index=0&sort_orderby=relevancy&sort_order=desc&post_facet_filters=%7B%22applicable_products%22%3A%5B%5D%7D

maybe,

In addition to the exquisite answers by Doug, whenever you need anything for print and screen/web use, the normal way is to create a CMYK version for print (unless you only wish to print on non PostScript office printers that inherently convert from RGB to CMYK) and also an RGB version for screen/web use (which also works for Word/Powerpoint templates).

Concerning the best possible quality of raster images for screen/web, the folowing may sound unforgivably outdated and boring, sorry.

If you wish to have PNGs (PNG24 (also (little) known as PNG32, it holds 24 bit colour and 8 bit Alpha channel (transparency)), of course) look crisp and clean, it is important to have the images in the exact desired final pixel x pixel size, forget about resolution which may actually lead to wrong sizes and hence blurriness. It is easiest and safest to work at the desired size.

A very common unsuitable way is to Export to PNG (remember to use PNG24 and use Transparency for artwork to be in front of different backgrounds) with a medium or high resolution, such as 300PPI.

And a common misunderstanding: (almost) 11 out of 10 times, a statement like "I created the document at 300 PPI" means that the value is chosen in Effect>Document Raster Effects Settings; however that only means that the (current) resolution of any raster effects applied to the vector artwork, such as (any kind of) Blur, is set to that value (and only unless/until the value is changed to something else); when zooming in, this resolution can be seen in contrast to and on the background of the vector artwork. So this setting has nothing whatsoever to do with the actual resolution of a raster image created from the (vector) artwork.

To retain the clean and crisp artwork, a PNG must be created at exactly the pixel x pixel size that it is to be used for, or at sizes that are powers of 2 times as large (2, 4, 8, and so on).

For clean and crisp artwork avoid JPEG.

It is also important to have the artwork and also the Artboard placed fully within integer/whole pixel X and Y values in the Workspace, which means that the X and Y values at the corners must be integer; this can be ensured by using one of the corner Reference Points in the Transform palette, and then checking that all the values X, Y, W, and H, are integer (the centre Reference Point can only be used if both W and H are even numbers).

Otherwise the resulting image will become a bit wider/taller and the extension(s) will be empty and therefore be (partially) transparent/white.

Therefore, the safest way is to create the artwork at the final pixel x pixel size and use a corresponding Artboard, then either use the Legacity Save for Web (where you can look in the Image Size window for size confirmation) or Export at 72PPI. In either case, use the relevant optimization (available with both ways); it is also convenient to have 72PPI in the Effect>Document Raster Effect Settings.

If you have pure vector artwork, you can relax a bit and have the artwork/Artboard at any size (the Artboard must have the same proportions as the final image), then use the Legacity Save for Web and set either Width or Height in the Image Size and Apply (make sure the other value is also correct).

The Legacy Save for Web may be an old carthorse, but it knows its way home, even if the driver is drunk and sleeping it off in the hay in the back.

I can assure you that however hard Illy (job description Adobe Illustrator) may have whipped you, it has been completely unintentional: she is always very friendly and eager to help. Some think that she sometimes, or always, moves in mystrerious ways, but once you really get to know her, your only regret will be that it took so long.