Building ethos depends not only on having good supporting evidence but also on identifying where the information is from.
Identifying sources of information in your speech is also called attribution.
Attribution functions to differentiate your thoughts and ideas from the information from reliable sources which you learned about in your research.
When you signal that your information is from a particular author or from a specific source you alert the audience to the fact that what you are saying is not your own original idea but is someone else's idea.
Students often present information without identifying the source of the information which means that a critical audience will begin to say to themselves "Says who?" or "How do you know?" This is particularly the case when the audience has a negative or skeptical attitude towards your topic or the speaker is not a known expert on the topic and so they must work harder to build credibility.
In order to benefit from the credibility that you will gain by identifying the source of your information you want to make clear to the audience that what you are about to say is from a reliable source and is not just something that is common knowledge.
You need to use "signal phrases" or "signal words" to alert your audience to the source of your information.
A typical signal phrase would be similar to the following:
Below is a list of some verbs that you can use to help you construct signal phrases
Rasmussen, K. (2003). A writer's guide to research and documentation (5th ed.). Upper Saddle River, NJ: Prentice Hall. p .7.
On the following websites you will find Basic Guidelines for attributing sources.
http://www.bucks.edu/academics/department/lang-lit/conference/citing/