The first battle is the introductory one, and doesn't have a point other than you getting the hang of what's going on. You will fight all of the battles as Goku. As you are Kami's student, he appoints this battle to you to test your skills and get ready for the big and fate-altering battles. The best strategy is to start by landing many smaller attacks on your opponent. The larger attacks will usually be dodged unless you weaken your opponent more. Also, make sure you leave enough Ki to perform some of the other moves you want to attack the clone with. You and the clone have the same amount of Ki and HP, so be wise with your moves. If you're having trouble with this battle, then you might want to go back to the main menu and try training some more.
When your SP bars fill up, you will be the first to attack, since yours fills up first. You can either choose to move or attack from where you are. The square in the top-right corner of the screen shows where you are and where your opponent is. Keep in mind that movement wastes the amount of moves you can execute in one turn. The first option is attacking your opponent physically, which requires you to be right in front of them. Your only available options will be "P1" and "K1", as in "Punch 1" and "Kick 1". Later on in the game, "P2", "P3", "K2", and "K3" will become available. For now though, steer clear of physical attacks, as you don't want to waste your moves. The second option is movement, with "+1", "+2", "-1", and "-2". Most obviously, this is moving closer or further away from your opponent. By choosing one of these options, the map will let you choose where you want to move. The third option lets you power-up your Ki, which has no other options behind it. You just restore a portion of your Ki and waste some of your moves. This would probably be useful if you want to execute energy attacks, which is the next option. These attacks regularly require Ki. The first option in the sub-menu is Ki Attacks. This will open up yet another sub-menu. There will be a regular Ki Blast and Kamehameha to choose from, and later on a Super Kamehameha and Spirit Bomb. Go back to the original sub-menu to see the other options—the Sun Flare which blinds your enemies, a special pattern technique, the Kaio-Ken which you acquire later on in the game, and Special Attacks. Special Attacks are like Physical Attacks, but they damage your opponent more and require Ki.
Choose any available move to attack your opponent with the result of them losing HP. Get your opponent's HP all the way down to 0 to win the battle. This may take awhile, but you have to be patient and choose your attacks wisely. After successfully attacking your opponent, you'll see the amount of HP they lost and how much HP they have left. By the time you're done with your attacks, your opponent's SP bar will be done filling up, and it'll be his turn to attack, which brings attacking to defending.
Defending is very different from attacking. You can either choose to block, dodge, or not try. Not trying should be your last resort. You should at least try to block or dodge your opponent's attacks. Selecting Block will bring you to a mini-game. There will be a long meter at the bottom of the screen and a ten-second timer. Press when the arrow is closest to the dark markers in the center of the meter. The closer to the center, the less damage you take. If the timer runs out before you can get to the middle, you will take full damage for the attack. There's also a Dodge mini-game. The Dragon Ball "Z" will be at the bottom of the screen, and an arrow can appear on either the left, right, top, or bottom of the Z. You have to press whatever side the arrow tells you to as quick as possible, or else the attack won't be dodged. To the right is a screenshot of Clone Goku attacking. The block option has been chosen.
Winning the Battle
Since this is just a practice match, it should be fairly easy. You shouldn't have anywhere below 100 HP when finishing the clone off. If so, more practice is recommended. After reducing his HP to 0, you'll win the battle and successfully complete practice. Now you can move on to the World Martial Arts Tournament.