I am new to dslr photography, i started with Canon 550d DSLR camera with efs 18-135mm kit. I am interested in macro and portrait photography. Can anyone tell me for which kind of purposes i can use my current lens and which lenses i need to buy for macro and portait photography.
If you are on the budget, you can try some m42 prime lens for Portrait photography. You can get some of the decent m42 lens for 20 to 50 USD over Ebay (Pentacon, Helios, Zeiss Tessar etc). Some of them cost much more as they are very sharp lens. Make sure that the focal length is from 50mm to 135 mm as they will give some great results for Portrait. Also, make sure that the aperture is 1.8 to 2.8.
However, keep in mind that these lens though cheap does not have auto focus so you have to do it yourself. For this you can get a EMF AF adapter for your Canon. It will cost about 10 USD but it will help to focus confirmation during manual focusing. You can also look for Canon 1.8/50 mm, a great lens to start with portrait photography. It will have AF and sharpness but less Bokeh (learn about it, if you don't know what it is). It will cost around 120 USD. I am also new to DSLR and on very tight budget. I got two m42 Manual focus lens from Pentacon (2.8/135mm and 1.8/50mm). Both are excellent in low light where our kit lens are almost unusable.
Macro Photography: You can get the Canon macro lens with AF (expensive), old macro lens (cheap but Manual focus), Macro filter (cheap but image degradation), extension tubes (AF is little expensive but manual is cheap) or reverse ring to mount the kit lens in reverse to decrease focal length and make it a macro lens to some extend (very cheap but depth of field is very shallow)