It is very difficult to give specific advice about writing an introduction without seeing the outline or notes of what is in your paper. Hopefully I can provide you with some tips to help get you started so that the introduction becomes more simple.
The first thing to remember is that you do not actually begin writing a paper with the introduction. In fact, I encourage my students to save the introduction until the very end (or just before writing the conclusion).
The writing process starts with pre-writing. This is where you gather ideas, questions you might answer in your paper, information (sources), topics you plan to cover, and specific examples you might include in your paper. Plan to spend a significant amount of time planning this paper.
Once you've done some initial planning, begin brainstorming several of the above elements more specifically. Include actual data and examples gathered from research. Though this is brainstorming, I actually encourage you to also begin organizing your data at the same time. Group similar ideas into categories. Though research papers are typically longer than the basic 5 paragraph essay, the organization is the same. Consider ideas in groups of three. Try to focus on three sub-topics of your big topic (English word formation). You may devote several paragraphs to each sub-topic (and split these subtopics further), but it is usually best to aim for three.
Once you've planned, brainstormed, and organized your data, you should be able to create an outline. I teach students not to write their thesis statement until their outline is mostly complete. Your thesis statement should be one or two sentences telling the overall purpose of your paper. Include your big topic and your three subtopics. This, in addition to any pertinent background information, reasons for the importance of your topic or a basic hook, will make up your introduction.
For a research paper of significant length, it is not unheard of to have an introduction that spans over several paragraphs. I hope this helps you get started. Follow the link below for more guidance and feel free to post further questions if you get stuck in the process.