For proper importing you need to set your CSV file settings:
- Delimiter
A CSV file uses commas to separate values, however many implementations of CSV import/export tools allow other delimiters to be used: semicolon, colon, tabulation, space. Use this drop-down list to select the character used to separate values in your CSV file.
- Encoding
Specify the encoding type used while saving your CSV file. The default type is UTF-8.
- Text Delimiter
Use this drop-down list to specify the character used to enclose the fields in your CSV file.
After that select the action which will be performed with the duplicate records in case there are some. Check the Skip option to import contacts keeping the existing contacts, use the Overwrite option if you wish to import them overwriting the existing ones or leave the default Duplicate option checked if you need to duplicate the coinciding contacts. You will be able to merge them later following the instructions here.
If your CSV file has a header row with the column titles make sure that the Ignore the first row when importing case is checked.