Тревогу (trevogu) means "alarm" or "anxiety." It's the accusative form of the noun тревога (trevoga).
In the song, the phrase "Моё сердце бьёт тревогу" (Moyo serdtse b'yot trevogu) literally translates to "My heart beats alarm." This vivid imagery conveys a strong sense of emotional intensity, suggesting the singer's heart is pounding with excitement and perhaps a touch of apprehension due to being deeply in love, as if for the very first time.
"Туда, Где Только Ты" (Where Only You Are) is a straightforward love song about wanting to disappear somewhere with one person and no one else.
The verses stay close to small physical details. Her gentle smile makes his heart beat faster, and he refuses to give up hope, because his whole soul belongs to her. Later he says roses opened in the garden because of her happy eyes, and that his own heart is sounding the alarm: he is in love the way he was the very first time.
The chorus is the promise. He is leaving for a place where there is only her and only him, and he cannot get through even a single day without her. The line "Ты слышишь, без тебя" (Do you hear, without you) comes back again and again, which is what makes the song feel less like a declaration and more like someone asking to be heard.
For learners, this is a friendly song to start with. The Russian is everyday and unhurried, the chorus repeats five times, and it gives you useful pieces you will meet everywhere: "я ухожу" (I am leaving), "не могу прожить и дня" (I cannot live even a day), and "ты слышишь" (do you hear).