Here you go - where i give you all parameters description in a more comprehensive manner
Wikipedia API help
format - The format of the output which is shown when you query in the url in your browser.(till now there is no better wiki format parser), so it will look like some junk content, and it takes only One single value:
json, jsonfm, php, phpfm, wddx, wddxfm, xml, xmlfm, yaml, yamlfm, rawfm, txt, txtfm, dbg, dbgfm action - There are various processes you can perform including sitematrix, opensearch, login, logout, query, expandtemplates, parse, feedwatchlist, help, paraminfo, rollback, delete, undelete, protect, block, unblock, move, edit, emailuser, watch.
version - this is used only When showing help which includes version for each module individually
maxlag - [actually dint work for me]
smaxage - here i gave 0,1, 2 and i found no difference
maxage - Set the max-age header to this many seconds. Errors are never cached
Default: 0
requestid - Request ID is used to distinguish requests.not that much important
here is a sample
api.php?action=query&prop=revisions&titles=Windows|Main%20Page&rvprop=timestamp|user|comment|contenthope this information helps.
Thankx to Roan Kattouw who is the person behind this API.. :-)