Prop up the bike so it can’t fall over and hurt you.
With proper tools, remove tire/wheel assembly,
Remove valve core from tube stem.
CAREFULLY, pry off tire and tube from wheel using 2 large flat blade screwdrivers.
Inspect tire for nail, thorn, whatever punctured the tire and remove it. Check for any other nails, etc. Be careful! You could cut yourself while inspecting tire!
Partially fill tube with air to locate hole. Buff area around hole with sandpaper, apply rubber glue, let dry, apply patch.
OR, replace tube.
Assemble tire to wheel being careful not to pinch tube with screwdrivers.
Partially inflate tube to insure the tube has not folded back on itself inside tire. Make sure tube filler stem points straight out.
Inflate tire fully while watching to make sure tire bead stays seated on rim of wheel.
Reinstall tire/wheel assemble on bike making sure wheel is aligned properly with front forks or rear swing arm and drive chain or belt.
If you’re not familiar with bike repair in this area, take it to the shop.