I can’t seem to gain any XP, I killed bosses in PVE, damages zombies in zombie mode, but the XP doesn’t go up.
Eff=0.00, this is your Experience Efficiency, and it acts as a multiplier by which you gain experience. Since your Eff=0, you essentially have no rate to earn Exp, hence why you have 0 Exp and are Level: 0. If you want to raise your Eff, you must purchase it using DP in the Trading Inventory.
In order to gain DP you must increase your Eff because of an affect called DP drain. You slowly lose DP due to having no Eff, so to mitigate its affect, you must have Eff>0. However, if you have 0 DP, you also start to slowly use your Eff.
Essentially, you have to farm a lot of DP and purchase a substantial amount of Eff (~10% or higher) in order to farm Exp. This truly is a time-investment for new players, especially since there really isn’t a good way to farm DP now-a-days, so good luck!
Also, one of the best sources of Exp is voting for the server with your username. Each time you do this, you also get lootboxes in your Trading Inventory. Note that the amount of Exp you earn from voting is also affected by the amount of Eff you have.