"Juxtapose," according to Merriam-Webster Online, is a verb that means "to place side by side." The two things being juxtaposed can be tangible and concrete, such as two different computers in a display, or more abstract, such as the opinions of two different politicians as presented in an article. 'Juxtapose' is often used figuratively to connect ideas or concepts. It does not mean to compare or contrast one thing with another, but things or ideas are often juxtaposed for that purpose.
Identify the two things that are connected. For example, imagine two scenes in a movie -- one showing a beautiful rural landscape and the other a metropolitan skyline with smog and traffic. Or imagine two passages in two different books that describe characters who have similar moral dilemmas, but deal with them in different ways.
Place the verb "juxtapose" in the sentence, using the correct verb tense after the two things being juxtaposed. For example, an appropriate sentence would read: "The scenes of rural beauty were juxtaposed with scenes of urban decay, implying that huge cities are a threat to nature." Another appropriate sentence would read: "If the two different passages are juxtaposed, we can see how the characters differ in their thinking about this issue."
Identify the active subject of the sentence if it is necessary to use the present perfect continuous tense, or "-ing." For example, if the active subject is a professor, an appropriate sentence might read: "The professor's lecture focused on juxtaposing the two different concepts of freedom in the debate on current political events."