Hello, i’m a beginner for blender. when I tried to extrude the handle of a cup, It is found the hold inner of the cup is produced. please check the picture.
hmm weird, try searching for duplicates
Mesh > Clean up > Merge by distance and then see if this still happens, it’s most likely not this but you never know.
oh wait, you are using solidify? then yeah you will get that, you have to apply the solidify and then do it
Welcome 
,
if you use the solidify modifier and extrude some faces then because there will be a hole at the extrusion location the solidification (?) may don’t work as expected. See by disableing the modifier.
If you close that whole it may be more what you want but the face at the hole will be smaller… so you may wan to apply the modifier first?..