This is the 15063rd most frequent Russian word.
поздравлять
To congratulate.
The word "поздравляю" is used in the present tense to express extending congratulations directly to someone.
Я поздравляю тебя с днем рождения.
I congratulate you on your birthday.
Here, "поздравляли" is in the past tense, referring to the act of congratulating someone for a past achievement.
Мы поздравляли её с успехом на экзамене.
We congratulated her on her success in the exam.
The verb "поздравлять" is used in the infinitive form as a general statement about the act of congratulating.