A control sequence in TeX starts with an escape character, which is usually mapped to the backslash character '\'. This is either followed by letters to form a control word, or by a single non-letter to form a control symbol. Control words are terminated by a non-letter, if this happens to be a space character then it is not used to effect the spacing of the document.
will end a paragraph. This is equivalent to a blank line to TeX.
will typeset an acute accent over an e followed directly by a grave accent over an a: éà