Bitcoin Nodes actions I have read the wiki page and I would like some further and more technical(if possible) confirmation for a few things. 
A bitcoin node is a user which is connected to the network through a client. This node can perform transactions, try to build a block inside a mining pool, or just exist in the network. Are there any further actions for a node?
If a node exists inside the network how can he verify the transactions?
Furthermore is there a paper or something that explains things in a lower level of how exactly the system works in case of transactions and mining? I do not want a description but something more technical.
A bitcoin node is a user which is connected to the network through a client. This node can perform transactions, try to build a block inside a mining pool, or just exist in the network. Are there any further actions for a node?


Nodes also relay blocks and transactions to other nodes. They also validate incoming blocks and transactions and keep track of the current, longest valid blockchain. That's pretty much it.


  If a node exists inside the network how can he verify the transactions?


There are a set of mathematical rules that determine if transactions are valid. The nodes check the transactions against those rules. If they meet the rules, they are valid.


  Furthermore is there a paper or something that explains things in a lower level of how exactly the system works in case of transactions and mining? I do not want a description but something more technical.


Almost every question you can think of is answered, in technical detail, somewhere in the Bitcoin wiki.