i have this problem: i want to sum all the sales of one person but
occurred many times using the SUMIF function. But i am not sure how to
do it since i am new to using this function. i have tried this
formula: =SUMIF(Sales,COUNTIF(Name,Sales),Name) but i am not sure if
this is right

For example:
Name Sales Region Commission Rate
Commission BERNIER $171,904 central 4.80% $8,251
BERNIER $171,904 north 4.90% $8,423
BERNIER $171,904 north 6.30% $10,830
BERNIER $171,904 north 6.00% $10,314
BERNIER $171,904 south 4.40% $7,564
BERNIER $171,904 west 4.50% $7,736
BERNIER $171,904 west 4.50% $7,736
BINCE $162,605 central 5.80% $9,431
BINCE $162,605 east 4.60% $7,480
BINCE $162,605 east 4.60% $7,480
BINCE $162,605 south 4.10% $6,667
BUSHBY $200,448 east 5.40% $10,824
BUSHBY $200,448 east 4.10% $8,218
BUSHBY $200,448 south 6.20% $12,428
BUSHBY $200,448 south 6.20% $12,428
BUSHBY $200,448 west 5.40% $10,824
BUSHBY $200,448 west 5.10% $10,223
CAMPBELL $259,500 north 4.30% $11,159
CAMPBELL $259,500 north 6.20% $16,089
CAMPBELL $259,500 north 4.30% $11,159
CAMPBELL $259,500 south 5.20% $13,494
CAMPBELL $259,500 south 5.20% $13,494
CAMPBELL $259,500 west 6.20% $16,089
CAMPBELL $259,500 west 6.30% $16,349

Here's an easy way, but it doesn't use the functions you mention.

With the names in column A, select that column and use
Data Filter AutoFilter
This lets you choose a person using a pull-down list in A1.

With sales numbers in column B, use this to calculate the sum:
=SUBTOTAL(109,B:B)