Right now the best thing that private citizens can do to help Ukraine is to donate money to organizations that address the humanitarian needs of the Ukrainian population and to put pressure on their governments to support Ukraine as much as possible. Some good organizations to support are CARE, RedCross-RedCrescent, the UN Refugee Agency, and UNICEF. There are also other organizations that deserve support. It is important to support these organizations NOW.
Of course, there is a strong desire to send weapons, but since most of us are novices at that, the best thing is to ask our governments to send weapons and whatever other support that they can send as soon as possible. We must help Ukraine deal with this atrocity NOW.