With the launch of Shadowkeep the progression system changed, and the older campaigns saw changes as well. All of the campaigns are now optional to play, rather than being required in order to progress to the newer content. All players are given access to patrols on every planet, which is why you are able to travel there. To start the Forsaken campaign, open up your Director, and then open the Tangled Shore map. Look for a large mission icon towards the bottom of the page, for the Last Call mission. Completing that mission activates the campaign, and will put the quest into your pursuits/quests page. You can access the year one legacy campaigns by visiting Amanda in the Tower Hangar, if you did not complete any of them previously, or just want to replay them for fun.

You are not a high enough light to start any dlc content. Go through the introductory quests and previous campaigns.