I downloaded a photo from internet and after cutting the part i don't want in Photoshop it got blurred. I am a beginner in Photoshop and i don't know how to make it in the best quality or at least in the same quality as i downloaded. Thanks in advance.
Most Internet images are low resolution or slightly blurry, or both. At small scaling, it is not too noticeable. Also the image could have jpeg artifacts which could be partially corrected.
First step is to look for a higher quality version of the image you want to work with. Then bring that image into Photoshop. Use Image Size_Resample_Enlarge to double or quadruple the pixel dimensions. Then Save As_tif or psd for your working copy. Later you can make a jpeg or whatever you need for output.
Zoom into the area you plan to crop and look for any faults. You may choose to sharpen. I use the Layer_Copy, High_Pass_Filter, Soft_Light_Blend method. You can also use the Clone Stamp to cover edge bubbles and other artifacts. Save this image, then crop and save as. You will keep the full image if you need to change the crop dimensions later.