Cleansing is fairly simple in concept. Places, items, and people all gather dirt and grime over time - physically and spiritually - and cleansing is simply getting rid of that gathered grime. Just as you wouldn't go without washing yourself for long periods of time, or invite your family over without tidying a bit first, it's good to also spiritually clean yourself and your spaces.
There are many different ways to cleanse, and it's really about choosing what's best for your situation, and something that won't damage the item you're cleansing.
The smoke of smudge sticks and other purifying incenses are quite popular. However, you could also dip an item in water with a bit of salt - or sprinkle that salt water onto the item, person, or around the place. Instead of salt water, a light tea of purifying herbs could also be used. An item might also be simple sprinkled in salt or herbs. The light of the sun is cleansing, and some use moonlight for the same purpose. You could pass an item over a flame. Use running water (a shower or bath is a good way to cleanse yourself both physically and spiritually). Sound can also cleanse - a sharking rattle, a tambourine, bells, flutes, or singing bowls can all be used to cleanse. Get creative and experiment with different methods.
When exactly to cleanse is also often a personal matter. Some always cleanse any space before holding a ritual, but in my personal practice this is not something I usually do when working outside. If a space doesn't feel right, I find a place that does. These places are not my home, and I would rather go where invited than try to push my way into a space, but this is something people will have different views on, of course. I cleanse my home about once a month, but I find doing it before every last working is not necessary as I have dedicated ritual space. Again though, it is really personal preference. Some do it more, some do it less.
When it comes to purification of items, I do this as needed, and always at Imbolc. Others do it once a month at the new or full moon. Some just do it only when it's needed.
As for purification of the self? This is easy enough to do with each shower or bath, if one wishes to do so. It can be nice to let all the spiritual gunk dissolve down the drain with the physical dirt. Taking a shower or bath before a ritual is common practice. At other times a ritual washing of the hands, and sometimes face or mouth is enough. Then there are times that you might be physically filthy, say if there's a long muddy hike to the ritual space, but a light spiritual cleansing of the self is still done as a gesture of respect.
To consecrate something means to dedicate it to a particular purpose, usually a sacred one. As with cleansing, there are many ways this can be done, but personally I prefer a fairly simple approach. After giving an item a good cleansing, I anoint it with a dab of blessed oil, and simply state what the item's purpose will be, and ask for the blessings of those it will be going into service of. I then spend a while meditating with the item, thinking about it's new purpose in my practice. It is then ready for ritual use.
In my opinion, it is only necessary to consecrate an item once if it remains in fairly active use. (For myself, that means at least once a year.) However, if a particular item had to go into storage for some time, or something like that, it certainly would not hurt to cleanse it and re-dedicate it.
Likewise, you might find you no longer need a particular item, or perhaps only needed it to act as a sacred tool temporarily. In either case, it's wise to remove it from service. Again, a simple way to do this is just by holding the item and saying some words to return the item to day to day use.
To charge an item means to imbue it with energy. This can be your personal energy, energy from the sun, moon, or other natural energy, or energy that you have raised and set to a particular purpose.
For example, if you wanted to make an amulet to use for protection, while crafting the amulet you would think of it's purpose. This begins to charge it. When it is complete, you would raise and focus energy as you would for any other working that required it, and it would then be focused into the item.
To charge an item with your person energy, you would simply have to spend time with it. This often happens on it's own with ritual tools we use frequently. To charge it with the energy of some natural force, you'd simply allow it to spend time in that force. Buried in the earth, under the sun or moon, hanging from a tree, dipped in ocean water, and so on. One might even ask a spirit or deity to bless an item with some of their energy.