Do

Do[expr,n] evaluates expr n times. 

Do[expr,{i,imax}] evaluates expr with the variable i successively taking on the values 1 through imax (in steps of 1). 

Do[expr,{i,imin,imax}] starts with i=imin. 

Do[expr,{i,imin,imax,di}] uses steps di. 

Do[expr,{i,{i1,i2,…}}] uses the successive values i1, i2, ….

Do[expr,{i,imin,imax},{j,jmin,jmax},…] evaluates expr looping over different values of j etc. for each i. 

Please visit the official Wolfram Language Reference for more details and examples on core symbols.