Que signifie What does celle and cel mean? And how do I use it?  ?

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Celle is the feminine of "celui". Celui and celle means the one.
Le garçon là-bas, celui qui est assis sur le banc, est triste. = The boy over there, the one who is sitting on the bench, is sad.
Celle qui veut aller avec moi, lève la main = Whoever (talking to a female) wants to go with me, raises her hand.
"Cel" doesn't exist in French.
There are also the plural versions :
Celui becomes "Ceux" in plural
and "Celle" is "Celles" in plural.
You can use those words even if you didn't specify who you are talking about as in "whoever" or to replace a noun you used before.

There is also a rule :
"This lamp, not that one, but this one" = Cette lampe, pas celle-là mais celle-ci.
We don't say cette-ci nor cette-là but celle-ci and celle-là.
Same for plural : These books, yes these ones over here = Ces livres, oui ceux-ci.