A competition is where two or more people try and be the best at something. The 'something' can be literally anything that can be judged on some critera of quality, like writing a story, running a race, baking a cake, or growing vegetables, like in the picture.
There is usually some kind of prize for winning a competition.
Something is first if it comes before all other things. When you win a race you come first. The picture shows the first of four candles alight.
Something is last if it is after all other things. For example, if you are at the end of a line of people you are last in the queue.
The picture is of the last bowling pin in a bowling game.
If you lose something, you do not know where it is. If you are lost, you do not know where you are. The picture is of a teddy bear someone has lost. Lose is not the same as loose.
The opposite of lose is find or win.
The past tense of lose is lost.
A medal is a small metal disk, usually round but sometimes in the shape of a cross or star. Medals are given to someone who has done something special, or as a prize for winning a competition.
A score is a record of the number of points, goals or similar made by one side during a game or competition. What you keep score of depends on the game being played. Scores are usually kept track of on a scoreboard, with a score for each of the teams shown on the board.
A trophy is something you are given when you win something like a competition. In war or when you are hunting, a trophy is something you take to prove your victory. In hunting, a trophy might be the head of an animal you killed, and in war it might be some possessions from the people you conquered.
You win something when you are better or faster at it than everyone else. You win a race when you cross the finish line first. You win an art competition when your picture is better than everyone else's. Your team wins a game like soccer if they score the most goals. And you win an eating competition if you eat more than everyone else.
The opposite of win is lose.