problem in welding vertices, a beginner I try to weld my vertices so its connected one by one but you can see here on the image I specified it doesn't turns out to what I wanted it to be, is there any solution for this type of problem?
Maybe you've chosen the wrong option from the Merge menu?
Make sure, of the selected vertices, the ones you want to be merged are closer to one another than to any others, and Merge &gt; By Distance

Or, if that's too fiddly, (and you want the merged loop to be centered to the ones above and below) select the edge-loops you want to be merged, and Ctrl E Edge Menu &gt; Bridge Edge Loops, with 'Merge' checked in its options.