I always remember it like this.
=index(THEANSWER,match(what your looking for,were the match is in the other table,0)
The 0 points towards an EXACT match see below if that helps?
<b>Excel 2003</b><table cellpadding="2.5px" rules="all" style=";background-color: #FFFFFF;border: 1px solid;border-collapse: collapse; border-color: #A6AAB6"><colgroup><col width="25px" style="background-color: #E0E0F0" /><col /><col /><col /><col /><col /></colgroup><thead><tr style=" background-color: #E0E0F0;text-align: center;color: #161120"><th></th><th>B</th><th>C</th><th>D</th><th>E</th><th>F</th></tr></thead><tbody><tr ><td style="color: #161120;text-align: center;">45</td><td style="text-align: right;;"></td><td style=";">Example 5</td><td style="text-align: right;;"></td><td style="text-align: right;;"></td><td style="text-align: right;;"></td></tr><tr ><td style="color: #161120;text-align: center;">46</td><td style="text-align: right;;"></td><td style="text-align: right;;"></td><td style="text-align: right;;"></td><td style="text-align: right;;"></td><td style="text-align: right;;"></td></tr><tr ><td style="color: #161120;text-align: center;">47</td><td style="text-align: right;;">1</td><td style=";">Match this</td><td style="text-align: right;;"></td><td style="text-align: right;;"></td><td style="text-align: right;;"></td></tr><tr ><td style="color: #161120;text-align: center;">48</td><td style="text-align: right;;">2</td><td style=";">Match that</td><td style="text-align: right;;"></td><td style="text-align: right;;"></td><td style="text-align: right;;"></td></tr><tr ><td style="color: #161120;text-align: center;">49</td><td style="text-align: right;;">3</td><td style=";">This is the match</td><td style="text-align: right;;"></td><td style="text-align: right;;"></td><td style="text-align: right;;"></td></tr><tr ><td style="color: #161120;text-align: center;">50</td><td style="text-align: right;;">4</td><td style=";">Match</td><td style="text-align: right;;"></td><td style=";">Lookup</td><td style=";">Result</td></tr><tr ><td style="color: #161120;text-align: center;">51</td><td style="text-align: right;;">5</td><td style=";">Example</td><td style="text-align: right;;"></td><td style=";">Match</td><td style="text-align: right;;">4</td></tr></tbody></table><p style="width:14.4em;font-weight:bold;margin:0;padding:0.2em 0.6em 0.2em 0.5em;border: 1px solid #A6AAB6;border-top:none;text-align: center;background-color: #E0E0F0;color: #161120">3. Index & Match Feature</p><br /><br /><table width="85%" cellpadding="2.5px" rules="all" style=";border: 2px solid black;border-collapse:collapse;padding: 0.4em;background-color: #FFFFFF" ><tr><td style="padding:6px" ><b>Worksheet Formulas</b><table cellpadding="2.5px" width="100%" rules="all" style="border: 1px solid;text-align:center;background-color: #FFFFFF;border-collapse: collapse; border-color: #A6AAB6"><thead><tr style=" background-color: #E0E0F0;color: #161120"><th width="10px">Cell</th><th style="text-align:left;padding-left:5px;">Formula</th></tr></thead><tbody><tr><th width="10px" style=" background-color: #E0E0F0;color: #161120">F51</th><td style="text-align:left">=INDEX(<font color="Blue">B47:B51,MATCH(<font color="Red">E51,C47:C51,0</font>)</font>)</td></tr></tbody></table></td></tr></table><br />