There are two ways to build a party, since the classes have a lot of overlap: Class and Role.
Generally speaking, Class gives people an idea of what you’re doing, but a Role defines it. Sometimes a cleric uses a crossbow, sometimes a rogue uses magic. A role lets the others know what you’re doing.
• Archmages are your general nukers, crowd control and AoE damagers. This is your man who solves problems with magic, often through a giant explosion of it. Defined most broadly as a “backline” caster who has little to no AC.
• Champions are the team captain and damage dealer. The Champion leads the charge and is generally hitting as hard as he can, either as DPS or a DPS/tank.
• Guardians are those who occupy a foe’s attention, either by tanking, distracting, or disabling. Resistances, immunities, save advantage, inflicting disadvantage, preventing escape, punishing disengagement… these are the tools of the Guardian; he keeps the baddies away from the back line of the party and from killing the Champion or Trickster.
• Hierophants are healers and buffers/debuffers; they generally have area effects which aid their allies, cast healing magic to keep the party on their feet, and create empowering boons to accentuate a strength. A hierophant provides areas of safety, as well as elemental protections and wards; they should really come across as a first aid kit, prepared to fix any manner of flagging weakness in their allies.
• Tricksters are those who want to remain out of the melee press until they deal their massive damage. They can disable foes by striking a hard-to-target weakness, undermine a foe’s advantage, and provide overwhelming DPS. Tricksters are often not able to take many hits, so they rely upon the Champion and Guardian.