Depends on the voltage.  Start with [https://www.allaboutcircuits.com/tools/trace-resistance-calculator/](https://www.allaboutcircuits.com/tools/trace-resistance-calculator/) to calculate the resistance of the tracks. If you are talking 100mA or more, always use multiple vias.  If in the Amps then make the vias much larger diameter than the default, or preferably put a component leg through the hole(s) so it is soldered solid. Never put vias under the actual SMT pins apart from large surfaces where they are designed to do this - for example SMT power transistors.  Instead make the pad larger and surround it with vias to transfer current and heat away. Select the component to go on the bottom layer and change the Layer menu item in top right corner to BottomLayer And never ignore DRCs.  It's a bad habit that will bite you at some time in the future.  Fix the problem even if it means changing the design a little.  A classic is the use of a 0 Ohm resistor so that two ground nets are separated.

hello with track width 2mm i draw a track on top and bottom .then i put some vias to connect top and bottom because i have 1A current,But so i have drc error. how can i do to do this without error ? thank you very much

Odd.  I do that all the time.  Try deleting the tracks and do the vias first, then the tracks.  It's definitely possible.