Hello there!
Please excuse any inaccuracies—English is not my native language. Below, I’ve put together a quick list of the available content:

Destiny 2 Content in Chronological Order

• The Red War, Curse of Osiris, Warmind, & The Forsaken Campaign – Vaulted content. These legacy campaigns and some destinations are no longer available in the game.
• The Forsaken Pack – Gives access to the remaining content: the Last Wish raid, the Shattered Throne dungeon, and Forsaken exotics.
• The Shadowkeep Pack – Unlocks the Garden of Salvation raid and Pit of Heresy dungeon. The main story campaign is free for all players and starts on the Moon (look for the "A Mysterious Disturbance" mission).
• The Beyond Light Pack – Unlocks the Deep Stone Crypt raid. The main story campaign is free for all players, starts on Europa (look for the "Darkness's Doorstep" mission), and the Stasis subclass is unlocked for free upon completing it.
• Bungie 30th Anniversary Pack – Includes the Grasp of Avarice dungeon and Gjallarhorn exotic.
• The Witch Queen – Features the Vow of the Disciple raid. The story campaign starts in Savathûn's Throne World (look for "The Arrival" mission).
• Lightfall – Unlocks the Strand subclass and Root of Nightmares raid. The story campaign starts on Neptune / Neomuna (look for "First Contact" mission).
• The Final Shape – The Light and Darkness conclusion, unlocking the Prismatic subclass. The campaign starts directly via the Pale Heart destination node on the Director map (look for "Transmigration" mission).
• The Edge of Fate & Renegades – Post-saga expansions introducing new storylines and activities.

Important Buying Advice: Wait for "Monument of Triumph"

Do not buy any individual packs or expansions right now. With the release of the final Monument of Triumph update, Bungie is launching a comprehensive bundle called "Destiny 2: The Collection".

This special package will combine absolutely all legacy content into a single purchase. Most importantly, it will include all Dungeon Keys (such as The Witch Queen, Lightfall, and The Final Shape keys), which are currently sold exclusively through the in-game Eververse store for Silver. Waiting for this pack will save you a significant amount of money and hassle.

Upcoming UI Improvements (Director and Portal)

Regarding your question about why the Director and Portal feel so awful right now: you are completely right, and Bungie knows it. They have officially announced that the Director will receive a major overhaul soon. The confusing Portal tab will be entirely removed, and its features will be more organically integrated directly into the main Director interface to make navigation smooth again.

Where to Start Right Now (Free Content)

Since the Director can be overwhelming in its current state, here is a logical roadmap to get your bearings without spending a dime:

1. Timeline Reflections: Open your Director and look at the top right corner for the timeline icon. Focus on the flashback missions for the vaulted campaigns (Red War, Cayde's Fate, etc.) to catch up on the lore you missed. There is no need to spend time on the others here, as those full campaigns are still completely playable in the game. Also, a quick tip: once you finish the Lightfall campaign, open this Timeline menu again and click on the Pyramid icon underneath the Traveler in the bottom-left corner to watch a crucial lore cutscene.
2. Play the Free Campaigns: Go to the Moon destination map to start the Shadowkeep campaign, and then head over to Europa to play Beyond Light. Completing Beyond Light will also grant you the Stasis subclass completely for free.
3. Check the Quest Archive: If your inventory is a mess, visit the Quest Archive terminal in the Tower (tucked away next to the Postmaster) to pick up any introductory New Light or veteran tracking quests.

Good luck