Ranger is a versatile medium armor profession that uses bows and other suitable weapons to hunt its enemies down. Ranger also has loyal pets to help the ranger and allies in the hunt by CCing, providing boons and tearing the enemies down. Ranger has lots of hunt-related utilities in its skill set, like survival skills and traps.
Ranger as itself has long been considered a DPS-class, condiranger still surviving as a popular build even for endgame content while power ranger hasn't been quite popular for some time. But with HoT, ranger got a powerful healer elite spec and with PoF, ranger gets a further boost in its DPS proficiency, especially power ranger.
With Heart of Thorns, ranger got a healing/support spec "Druid" that lets ranger use staff as a new weapon.
Druid collects astral energy by damaging foes and healing allies and when the astral energy is full, druid can become Celestial Avatar to use strong heals. Druid added glyphs to ranger's utility skills, with each glyph having different effect depending on whether it was used in normal form or Celestial Avatar.
As such and with the support capabilities ranger already had, druid became the community's choice of healer for any challenging stuff, thanks to its strong heals and especially all the offensive support traits and utilities it has.
With Path of Fire, ranger gets another damage-focused spec "Soulbeast" that gives ranger the ability to use dagger as main-hand weapon. Soulbeast merges with pet and gains it's powerful skills to use while also gaining stats according to pet's nature, like power and ferocity from merging with a Ferocious pet. Soulbeast adds new Stance-utility skills that grant the soulbeast various boosts when used. When soulbeast has merged with a pet, all pet-related skills and traits work on the soulbeast itself, which leads to some interesting and extremely powerful results (for ex. Sic 'Em as power soulbeast adds insane damage boost and if you combine it with a couple other boosts, you might see hilarious damage numbers...) .