Your level increases with XP. How much XP you need for your next level can be found on
https://www.warzone.com/wiki/LevelsYour XP can only go up, so you will not lose XP for losing.
Surrendering/booting/getting eliminated all just count as "losing" and are treated the same.
The XP you earn for a game is based on a number of factors, those are described on the wiki as well:
https://www.warzone.com/wiki/PointsTo summarize the wiki:
• Real-time gets lets XP than multi-day
• Coin, tournament, and ladder games are worth extra XP
• XP is based on the level of your opponents and your own level
• How long the game took or how you won it doesn't matter
• You get reduced XP if you beat the same player regularly
As a side note:
WZ is a primarily English game, with everyone using English to communicate.
You should probably try using English as much as possible, as very few people will bother translating what you say to English.
