it happen some to say too many times bzH and write. what does it mean saying in vain and how to understand borderline between saying holy names and not to say in vain?

ב"ה Shalom The prohibition of saying Hashem's name in vain means saying G-d's name for no purpose. It is learned from the Passuk "you shall not utter the name of G-d your Lord in vain..(Shemot 20:7) For example, you may not say G-d's name not part of Tefilla or Torah learning , or even if it is part of tefilla but it is said unnecessarily. The names included in this prohibition is not just ineffable name of Hashem, Yud- K- Vuv-k, but the additional 6 names which are also not allowed to be erased as enumerated in the Shulchan Aruch Yoreh De'ah 276:8. (See also (משנ"ב סי' רט"ו ס,ק יט, קיצור שולחן ערוך ו:ג, such as E-l, Elokim, etc. whether it is in Hebrew or in any language. Using the name Hashem, is no problem. The name Hashem means "the name" . It is our solution of referring to G-d without having to use his real name. Therefore, there is no problem in saying "B'e'zrat Hashem etc. For more details see also: https://halachipedia.com/index.php?title=Not_Saying_Hashem%27s_Name_in_Vain All the best