As players repeat certain actions, they will gain “Skill Experience”. When the player reaches certain amounts of XP for a given skill, they will achieve higher levels for that skill.
Every 5-10 levels (referred to as milestones) will unlock the ability to use new types of items, tools, weaponry, and armor.
This is roughly the idea of what these milestone levels will unlock.

(gilded and stylized variants are for premium members only)
(gear for premium members is equal to gear for free members)
Melee, Mining, Woodcutting & Smithing Milestone Order:
5: Bronze
10: Steel
20: Diamond (available in gilded and stylized)
30: Netherite (available in gilded and stylized)
30: Aetherite for premium members (available in gilded and stylized)
40: Obsidian (also requires 30 strength to wield/wear or 60 crafting to create)
50: Mithril (available in gilded and stylized)
55: Tier 1 special items (not craftable) (some have other level requirements) (some require premium membership)
60: Adamantine (available in gilded and stylized)
60: Lumerite and Veridite for premium members (available in gilded and stylized)
65: Enderite
65: Pavonite & Vicronite for premium members (available in gilded and stylized) (not craftable) (Pavonite also requires 65 magic and defence for melee. Vicronite also requires 65 magic and strength for melee)
70: Vibranium (because marvel reference)
70: Orichalium for premium members (not craftable) (some require premium membership)
75: Tier 2 special items (not craftable) (some have other level requirements) (some require premium membership)
80: Tier 3 special items (not craftable) (some have other level requirements) (some require premium membership)
85: Tier 4 special items (not craftable) (some have other level requirements) (some require premium membership)

Archery & Bowmaking Milestone Order:
0: Regular wooden bows and crossbows
5: Iron bows and Bronze crossbows
10: Steel bows
15: Steel crossbows and composite bows
20: Composite bows
25: Javelins
30: Mystic and Abyssal composite bows for premium members
35: Netherite crossbows
35: Aetherite crossbows for premium members
40: Explosive Bows
45: Sniping crossbows and Ballistas
50: Chemical Assault Bows
50: Lumerian bow for premium members
55: Mithril crossbows and Veridian blowpipe
55: Semi-auto crossbows for premium members
60: Tier 1 special bows (not craftable) (some have other level requirements) (some require premium membership)
60: Blast Bow for premium members
65: Adamantine Crossbow
70: Ender Bow for premium members (not craftable)
70: Pavonine & Vicronian bows for premium members (not craftable)
75: Custom crossbows
80: Tier 2 special crossbows (not craftable) (some have other level requirements) (some require premium membership)
85: Tier 3 special crossbows and bows

Magic items have not been added to this list yet. I’m not even sure if it’s possible and/or practical to add magic as a combat style