Please use cd .. to go back to the top directory of the tutorial material. Then, change to the directory exercise_2.
In the directory exercise_2/, you will find a text file solution_2.1.txt. The fifth character is inside that file. To see its contents, use the command
more <filename>
To get character number six, you will need to create a text file in the exercise_2 directory. On Ubuntu, you can do this using the editor gedit. You can start it typing the name of the program, or
gedit <filename>
Create a text file with a name of your choice in the exercise_2 directory that contains the phrase
Please give me solution 2.2
Afterwards, run the program
./text_file_check
If you want to know more about a particular command, type
man <command>
You get shown a help page that you can leave by pressing 'q'.