I was looking at other peoples rune pages and saw that their runes had the corresponding borders for their runes, but I didn't.

My runes all have a red SECONDARY text and red borders. what does that mean?

Different runes are more or less effective depending on what rune type they are. For example,a glyph of insight (magic pen) will have a red border because marks (red runes) are the primary runes for magic pen. Primary runes are more powerful than their secondary or tertiary counterparts, although if you are trying to load up on one stat you may still use the latter.

Yes, this is primarily to give you diminishing returns if you are trying to max/min your champion by getting one stat really high... not necessary a bad idea.

However, if you use primary runes for all three types, you will get bigger stat boosts for your space, but it will be spread out over different stats.. Better for well rounded builds and newer players in my opinion, unless you have a super specialized build in mind.

How do I know which is considered primary/secondary/teritiary? I hover my mouse over the runes in the store and it really doesnt say.

It isn't stated, but here's how it's done. Every stat has a primary rune.

Marks specialyze in offence, seals in defence, glyphs in magic.

So runes that give armor penetration would be primary marks (red), health is primary for seals and AP is primary for glyphs.

If you're interested in a stat just check all the runes to see which one gives the most, for the most stats it should be easy to see if it's offence, defence or magic.

Quintescences specialyze in Utility, but they give fairly high bonuces from every stat.