added a getting started section

docs/source/getting-started.md

@@ -1,3 +1,128 @@
 # Getting Started
 
-Some short examples of using BigchainDB, i.e. short tutorials.
+With BigchainDB and rethinkDB [installed and running](intalling.html) we can start creating and
+transferring digital assets.
+
+##### Importing BigchainDB
+
+First, lets open a python shell
+```shell
+$ python
+```
+
+Then we can import and instantiate BigchainDB
+```python
+from bigchaindb import Bigchain
+b = Bigchain()
+```
+
+When instantiating `Bigchain` witouth arguments it reads the configurations
+stored in `$HOME/.bigchaindb`
+
+
+##### Creating digital assets
+In BigchainDB only the federation nodes are allowed to create digital assets
+using the `CREATE` operation on the transaction.
+Digital assets are usually created and assigned to a user, which in BigchainDB
+is represented by a public key.
+
+BigchainDB allows you to define your digital asset as a generic python dict that
+will be used has a payload of the transaction.
+
+```python
+# create a test user
+testuser1_priv, testuser1_pub = b.generate_keys()
+
+# define a digital asset
+digital_asset = {'msg': 'Hello BigchainDB!'}
+
+# a create transaction uses the operation `CREATE` has no inputs
+tx = b.create_transaction(b.me, testuser1_pub, None, 'CREATE', payload=digital_asset)
+
+# all transactions need to be signed by the user creating the transaction
+tx_signed = b.sign_transaction(tx, b.me_private)
+
+# write the transaction to the bigchain
+# the transaction will be store in a backlog where it will be validated,
+# included in a block and written to the bigchain 
+b.write_transaction(tx_signed)
+```
+
+##### Reading transactions from the bigchain
+
+After a couple of seconds we can check if the transactions was included in the
+bigchain.
+
+```python
+# retrieve a transaction from the bigchain
+tx_retrieved = b.get_transaction(tx_signed['id'])
+
+   'id': '6539dded9479c47b3c83385ae569ecaa90bcf387240d1ee2ea3ae0f7986aeddd',
+   'transaction': {   'current_owner': 'pvGtcm5dvwWMzCqagki1N6CDKYs2J1cCwTNw8CqJic3Q',
+                      'data': {   'hash': '872fa6e6f46246cd44afdb2ee9cfae0e72885fb0910e2bcf9a5a2a4eadb417b8',
+                                   'payload': {'msg': 'Hello BigchainDB!'}},
+                      'input': None,
+                      'new_owner': 'ssQnnjketNYmbU3hwgFMEQsc4JVYAmZyWHnHCtFS8aeA',
+                      'operation': 'CREATE',
+                      'timestamp': '1455108421.753908'}}
+```
+
+The new owner of the digital asset is now
+`ssQnnjketNYmbU3hwgFMEQsc4JVYAmZyWHnHCtFS8aeA` which is the public key of
+`testuser1`
+
+
+##### Transferring digital assets
+
+Now that `testuser1` has a digital asset assigned to him he can now transfered it
+to another user. Transfer transactions now require an input. The input will a
+transaction id of a digital asset that was assigned to `testuser1` which in our
+case is `6539dded9479c47b3c83385ae569ecaa90bcf387240d1ee2ea3ae0f7986aeddd`
+
+```python
+# create a second testuser
+testuser2_priv, testuser2_pub = b.generate_keys()
+
+# create a transfer transaction
+tx_transfer = b.create_transaction(testuser1_pub, testuser2_pub, tx_retrieved['id'], 'TRANSFER')
+
+# sign the transaction
+tx_transfer_signed = b.sign_transaction(tx_transfer, testuser1_priv)
+
+# write the transaction
+b.write_transaction(tx_transfer_signed)
+
+# check if the transaction is already in the bigchain
+tx_transfer_retrieved = b.get_transaction(tx_transfer_signed['id'])
+
+{   'id': '1b78c313257540189f27da480152ed8c0b758569cdadd123d9810c057da408c3',
+    'signature': '3045022056166de447001db8ef024cfa1eecdba4306f92688920ac24325729d5a5068d47022100fbd495077cb1040c48bd7dc050b2515b296ca215cb5ce3369f094928e31955f6',
+    'transaction': {   'current_owner': 'ssQnnjketNYmbU3hwgFMEQsc4JVYAmZyWHnHCtFS8aeA',
+                       'data': None,
+                       'input': '6539dded9479c47b3c83385ae569ecaa90bcf387240d1ee2ea3ae0f7986aeddd',
+                       'new_owner': 'zVzophT73m4Wvf3f8gFYokddkYe3b9PbaMzobiUK7fmP',
+                       'operation': 'TRANSFER',
+                       'timestamp': '1455109497.480323'}}
+```
+
+##### Double Spends
+
+BigchainDB makes sure that a digital asset assigned to a user cannot be
+transfered multiple times.
+
+If we try to create another transaction with the same input as before the
+transaction will be marked invalid and the validation will trow a double spend
+exception
+
+```python
+# create another transfer transaction with the same input
+tx_transfer2 = b.create_transaction(testuser1_pub, testuser2_pub, tx_retrieved['id'], 'TRANSFER')
+
+# sign the transaction
+tx_transfer_signed2 = b.sign_transaction(tx_transfer2, testuser1_priv)
+
+# check if the transaction is valid
+b.validate_transaction(tx_transfer_signed2)
+Exception: input `6539dded9479c47b3c83385ae569ecaa90bcf387240d1ee2ea3ae0f7986aeddd` was already spent
+
+```