There is no single-player campaign mode in Escape from Tarkov. There is, however, an offline mode. The offline mode is meant for practice against and with AI players. Ideally, you will practice in the game’s offline mode before heading online. Playing the game this way ought to give you an understanding of the maps and feel of different weapons before you take it all on in an unfriendly online setting. There is technically a single-player mode in Escape from Tarkov, then, but it is not a story/campaign mode. It is planned, though, that story quests of some kind will be added into the game at some point.
We don’t know when the story quests will be added to Escape from Tarkov, nor do we know what form they will take. We might see campaign quests that tell a story during online play, for example. Sides to the main of the online modes. The planned story quests could come in the form of single-player levels, too. All we know is that as of May 2020 (as per this Reddit thread), Escape from Tarkov story quests are planned. No time-frame or further details have been given as of writing.
For now, the only Escape from Tarkov single-player offering is the game’s offline mode, which is meant for practice. We’ll have to wait and see if a full single-player story/campaign mode is added to the game in the future.