The first step to teaching your kindergarten students to write is to expose them to books that model good writing. In addition to reading aloud, you should be doing one-on-one guided reading with your students and small-group reading. Have the students point to the words as you read them. Point out the capitals and the punctuation.
Your students do not need to understand the structure of a sentence to start writing. They don't even need to know how to write all of the letters. Provide at least a few minutes each day when your students are able to free write. Students should write about what they want in the best way that they are able. This means that some students may have actual sentences while other students mostly scribble.
Your students' first exposure to sentence writing should be simple. Start the sentences and have your students finish them. A few common starters are "I like," "I can," "I am" and "I want." Your students will build confidence in their writing abilities as they continue to write predictable sentences on their own. As your students write, remind them that sentences begin with a capital letter and end with a period.
Once your students are comfortable with predictable sentences, they can begin adding more descriptions. Instead of "I like ice cream," have your students explain what kind of ice cream. For example, "I like strawberry ice cream with sprinkles and whipped cream on top." Explain to your students that a period at the end of a sentence can be replaced by a question mark when you are asking something or by an exclamation point when you are excited about something.