"I will go to university yesterday." 

'Yesterday' is a temporal adverbial modifier that refers to the past. In your sentence, you said that you are going to university and that is a future plan, or something that is happening right now or will happen soon. So, the construction "will + go" cannot have 'yesterday' with it. Try "I will go to university this year", so as to refer to a future moment. 

Also, "three country".

Country is a countable noun and when using its plural form (as in your example) you need to add the suffix -s to it. Like this: country + s = countries. Because the word ends with a "Y", when we add the suffix for the plural (which in this case is not a clean -s, but rather -es) we change it to an "I". The final result is countries.

country + es = countries