The Messenger of Allah (sal Allahu alaihi wa sallam) said “Allah has ninety nine names, one less than a hundred, whoever perfects them enters paradise”.
[Sahih Al-Bukhari and Sahih Muslim]
The Prophet (sal Allahu alaihi wa sallam) mentions in this hadih that Allah Almighty has 99 names and whoever perfects these 99 names enters paradise. Allah’s names are not restricted to 99, what this hadith means is that whoever perfects these (specific) 99 names enters paradise.
The meaning of “perfecting” Allah’s names is to affirm them, memorize them and understand their meanings.
And Allah Knows Best!