You can only put certain runes in their respective slots:
- Seals are Yellow
- Marks are Red
- Glyphs are Blue
- Quints are the 3 big brown slots
Along with that, each color of runes (Seals, Marks or Glyphs) usually tend to lend more to one area of increasing stats.
- Red marks usually increase offensive stats
- Yellow Seals are usually defense, utility or general all-rounders
- Blue Glyphs are utility or sometimes lesser used as extra defense
- Quints are used for your big spikes of stats that you want to focus your rune page around
For a beginner were not going to get overly complex into specialized rune pages, but you should start with:
- 9x Tier 3 Flat Armor yellow seals
- 9x Tier 3 Flat Attack Damage red marks
- 9x Tier 3 Hybrid penetration red marks
- 9x Tier 3 Flat Magic Resist blue glyphs
- 3x Tier 3 Flat Attack Damage Quints
- 3x Tier 3 Flat Ability power quints
with two pages, make one only for Attack damage and the 2nd one only for Ability power and the hybrid penetration
You probably won't jungle well (or maybe shouldn't yet) but atleast you got 2 areas covered for general champ types.
Not gonna lie, runes get expensive since you have to use IP and that gets sucked up quick early on when you just start out.
Don't buy anything under tier 3 runes, because once you're level 30 you will never use those tier 1/2 runes again.