Why all my clefs have number 8 at the bottom.

Some instruments (such as guitar) sound an octave lower than notated and use an octave clef.
See:
https://en.wikipedia.org/wiki/Clef#Octave_clefs

And tenor voice too, that's the case here apparently

So, it's normal/correct that music written for tenor voice would be in treble clef with the 8 to indicate it actually sounds an octave lower. If you don't want it to sound an octave lower than written, simply change the clef to standard treble using the Clefs palette. Then it will display at the same pitch it is written. Music for tenor will be very low for tenor clef - lots of ledger lines below the staff. So you might consider changing to bass clef instead if you really want it to be written for tenor. Or, if you actually want it written for soprano, transpose everything up an octave (Ctrl+A to select all, Ctrl+Up to transpose). And in the future, select "Soprano" instead of "Tenor" when creating your score.