A sonnet consists of a 14 line poem which follows a very precise pattern and usually in iambic pentameter: 3 four line units called a quatrain and then the end which is a rhymed couplet or two rhymed lines. The ideas are all related to one theme though different ideas in each quatrain and then the couplet provides the conclusion.
As for teaching the sonnet to your students, your question does not include the age of your students. When I began this process for my students, I needed to teach the very basics of stressed and unstressed syllables which I did using their names. Then we scored a line which the class created, showing the stressed and unstressed syllables. When they understood that idea, we looked at several couplets, chose one, and wrote out the pattern of the syllables, referenced the imagery used and its purpose, and how the writer created the whole from the parts. When they could each understand the patterns, we did one sonnet together as a class so that each student or group could clarify questions. When that was accomplished, I handed out one sonnet for each group of four, asked them to write out the pattern, and then analyse the theme being presented in the sonnet. When they could understand the technical pieces to a sonnet, we began our study of sonnets with Shakespeare's and then perhaps introduced other writers of sonnets. When we had discussed several in group settings, we discussed them as a whole class. The final assignment was to write one sonnet together in their group of four which forced them to USE the skills they had learned. Words had to be carefully chosen, the theme had to work with the quatrains, and the ending couplet had to truly express the conclusion of their theme. I found that the study of sonnets was helpful, but that the writing of one in a group where each wrote their ideas or lines in different colors, was the one thing which really helped them understand what a sonnet is and why Shakespeare's sonnets show his genius. Whatever the age of your students, and I am assuming they are not yet college students, be sure to carefully choose the sonnets you use as some are far easier to analyze than others. Because mine were not college students, the sonnets took more time than other topics studied.