You can also use an array formula to do this.

If you have ABC:DEF:GHI in cell A1 then if you enter the following formula in B1:D1 it will split out the text in A1 by the colon character.

=IFERROR(MID(":"&$A1&":",SMALL(IF(MID(":"&$A1&":",ROW($1:$999),1)=":",ROW($1:$999),""),COLUMN()-1)+1,SMALL(IF(MID(":"&$A1&":",ROW($1:$999),1)=":",ROW($1:$999),""),(COLUMN()))-SMALL(IF(MID(":"&$A1&":",ROW($1:$999),1)=":",ROW($1:$999),""),COLUMN()-1)-1),"")

You need to hit CTRL+ENTER to enter the formula.
The main part that is repeated 3 times is this bit...
IF(MID(":"&$A1&":",ROW($1:$999),1)=":",ROW($1:$999),"")
which gets an array of the positions of the colon (using the rows 1 to 999 although you could use more). This returns the array

1;"";"";"";5;"";"";"";9;"";"";"";13;"";"";""

Using the SMALL function you get the 1st and second smallest values which gives you 1 and 5. Then it uses the MID function to get the string between the first and 5th characters (bearing in mind the string is ":ABC:DEF:FHI:" because we added the separator to the beginning and end). Then in the next column you get the text between the 5th and 9th characters etc.