[sql] indexing options

[Robert Brenstein]

When I have a query like

Select * From blahblah Where fld1 = 'word1' and fld1 = 'word2'

what are the advantages/differences from having fld1 indexed by words 
versus normal indexing?

I understand that using regex (LIKE search), I search for substrings 
not full words (unless I use grep to define search more), but I 
realized that I am not 100% clear on different indexing options for 
normal queries.

Robert