In CMYK each colour is applied in turn, the inks start to mix together, and we start to form our image. K being the key colour which blends together the cyan, magenta and yellow inks.
In Illustrator, using the swatch palette, you can consistently use the same colour throughout.
You can also delete swatches from the palette, to simplify your workspace.
You can set a new swatch by clicking the new swatch button. - Lots of different ways to do the same things, selecting colour, all of which are relevant.
When applying colour without using the swatch palette, perhaps reverse engineering a piece of work, you can select the add used colours in the drop down menu, which adds all the colours in the document. If you select specific items in the document you can add them, only.
These colour swatches will have a white corner on icon, this means the swatch is global.
When global is selected, the colours to which the swatch is applied to will change if you were to edit the swatch, it will update in real time.
Global allows you to work with tints of that colour. You can then create tint swatches.
If you then edit the 100% swatch, all the tints created from that swatch will update.
Process Inks refers to CMYK
Spot colour is it's own individual ink, it's not created using CMYK. A spot color is a specially mixed ink using in printing. Spot color inks come in a rainbow of colors, including some specialty inks such as metallic and fluorescent.
Unlike CMYK or process colour which creates colours by laying down layers of just 4 specific inks, spot colours are pre-mixed and you use one ink for each colour in the publication. You can also use tints of a spot colour to get the appearance that you're using more colours without the expense of additional inks. For example, if you needed a specific colour for a brand, you would get a spot colour - if you were to work for EE you would get the turquoise used across the brand. You can choose these with Pantone Swatches.