Can you help me write a Shakespearean sonnet and write a few lines please?

Help, yes. Write, no.

You have to decide what you are going to write your sonnet about before any lines can be written. Maybe your assignment contains a theme for the sonnet. If it doesn't, think up a two part sentence connected with the Word "but". For example "I wish I could eat chocolate bars but I have a peanut allergy", "Wool shirts are so warm but they are also itchy", "Listening to music loud can hurt your ears, but it is totally worth it", "I would like to be an actor but I haven't got the courage." You will say the part before the Word "but" in the first eight lines or so of your sonnet, and the part after the Word "but" in the last six, more or less.

OK, once you have decided what you are going to write about, you need to get a feel for iambic pentameter. To do this I recommend listening to as much as you can--don't read it, because you can't get the rhythm that way. Listen to people reading Shakespeare's sonnets on YouTube, or a Shakespeare movie with the original dialogue (not Much Ado About Nothing which is not in iambic pentameter). Then start trying to say things in that rhythm. Don't worry about rhyming, or saying something profound. "I think I need to go and take a pee", "Could you please pass the salt and pepper please", "I wish I could afford that pair of shoes" are all in iambic pentameter. You can think up longer sentences which are two lines of iambic pentameter.

Now you start talking about your theme. You will be able to create and discard a number of possible lines until you find some which describe your theme, are in iambic pentameter and also rhyme. The strong sounds at the end of the lines are usually ones which are easy to rhyme: if your poem starts "I think I need to go and take a pee;/ My bladder gives me sharp and constant pain." you have two easy sounds to rhyme your next two lines to.