Jump to specific character in a line in VI

I'm not 100% sure of the meaning of the question, but if (for example) you want to find the next 'a' on a line, you'd type 'fa' (in command mode). That finds the next 'a' to the right. 'Fa' would find the next 'a' to the left.

The other way I can interpret your questions is that you want the cursor on a particular column. number| puts the curson on column number in the line the cursor already appears on.

if you want to go to the 12th character on a line:

12|

For the 6th character in the line:

6|