Constantly getting ‘cancels Clean Self: Area inaccessible.’ messages

A few things may be preventing your dwarves from eating the available food or drinking the available alcohol. The main two culprits are:

• No path available to the item or its container.
• Dwarves aren't permitted to travel where the food and drink is located.

Other things that stop dwarves from eating and drinking:

• The food isn't edible to dwarves. Examples: Seeds
• The drink isn't drinkable. Examples: Milk (shows up as other in foodstocks)
• The item is forbidden.
• The food or drink is claimed by a militia member as part of his/her food rations.

The dwarf fortress wiki has extensive articles on how to grow food, how to collect plants to eat or process (ie, cook in a kitchen) into edible food items, how to set up a still, etc. I'd suggest you look up plant collecting, still, food stock, and above ground farming. It is possible to farm underground, which uses a different set of plants (they can only be found in underground caverns or traded for with dwarven caravans) and requires easy soil layer access or making mud which sounds like it would just be an extra complication for you at this point in your dwarf fortress experience.

Mining is only a designation for the current Z-Level. The world of DF is divided in slices called a Z-Level, and you need to use stairs or ramps to go from a level to another. Here, you are telling your dwarves to mine tree and open air... Not very useful

You should designate for mining in a black area like at the top of your screenshot. These areas are underground, where you can dig directly without having to go up or down.

If you really want to go down, dig one down staircase and one up staircase just bellow (use < and > to move between levels), or dig a channel, which is a kind of "dig the ground just bellow" command.