Please help, how much is the effect of alcohol on my fitness level?

Depends : On how much & how often you indulge, & your general fitness level. In general, alcohol is a "depressant." and, as such, the altered sensorium, fatigue, potential malnutrition and lack of energy that ensues can affect your workouts adversely. That said, a glass of wine or beer socially or now & then probably won't affect your fitness level unless your health is compromised for other reasons.