Let's be honest, many creatives don't really make the difference between Spacing and Kerning. It's simply because both share the same goal: get a harmonious rhythm of space between letters for any character combination. And it is a 2-step process.
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Spacing is about defining for each glyph the amount of whitespace on its left and right sides. These two values - called sidebearings - depend on the shape exposed by the glyph on each side. The "straighter" the side is (like for H, I, N or left of B, L,...) , the larger the sidebearing is.
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A traditional process applied by many type designers is to start with straight letters like H (or n). It lets you define a rhythm for your font. Then continue with curved letters like O (or o) and go further until concave letters like T, X, V, Y or Z.

Let see a sample font before spacing:

and after spacing:

Look better, isn't it!
But the job is not done. There are still many pairs of letters which look bad:

Although A, V and T have been well spaced, the combinations AT, AV, VA (and many others) need further adjustments. It's time for Kerning.
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Kerning lets you define whitespace correction for specific pairs when it's needed. Of course, AV, AT, or VA are the usual suspects like in our prevous sample: 

But as you can imagine now, a professionnal font require thousands of pairs for all combinations that may need correction (Letters/Letters, Letters/Punctutation, ...). It's hours, sometimes days, of work for a trained eye to kern a font.
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The good news here is that, since v3.5, Fontself Maker lets you get your font Spaced and/or Kerned in one click. 

Of course it will never replace the trained eye of a professional type designer, but for most cases, it gives you a very satisfying result, saves you hours of work and lets you release your font faster.

First, Fontself Maker precalculates a sidebearing value around straight letters like H (remember, it defines the rhythm of your font). Of course you can adust this value. Based on it, Fontself Maker automatically spaces all other glyphs.
Once Spacing is done, Fontself Maker groups your glyphs into kerning groups, and finally computes all the kerning pairs needed by your font. 

Et voilà!
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if you want to have more control on these two steps, you can perform them separatly in Spacing and Kerning Advanced views and even make some fine tuning.
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Otherwise, enjoy the spare time ;)  
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