We suposse you have interest in Oracle and databases in general, but, how succeeding as a DBA? this are some suggestions.
There is no easy way to achive this, requires spend lot of time reading and practice, dba carrer is about read lots of documentation, understand documented concepts, and apply them to real-world tasks.
1) If you are starting, first target: Concept Guide, get into the docs: http://tahiti.oracle.com/ and dowload your first oracle guide
the Concept Guide: http://docs.oracle.com/cd/E16655_01/server.121/e17633/toc.htm
Start reading and understanding concepts like: RDBMS, Database and instance, arcitecture picture, storage structures
(datafiles, redolog,controlfiles,etc..),Pfile,Spfile, Logic structures(Blocks, Extensions, Segements and Tablespaces).
Segments Types, objects(Tables,Index,etc..) Memory structures (SGA,PGA) Background Process(pmon,smon,lgwer,chkp),etc..
Install a test enviroment, VM and go with this tasks: install a DB, create a hot backup, create a cold backup, restore from each backup, install a patch, install a patchset, duplicate the database, create a SQL query to fetch some data from the sample schemas (describe what to extract), create a PL/SQL procedure to i.e. receive value as an input and create a table named as the input variable, use exp and expdp to export data and import them in another database. Add more tasks as you go, make tasks more complicated by adding extra requirements if they are too easy.
Most important for a DBA: Backup, backup & backup. Secure data is the main objective, asure that data will remaind when disaster
3) OTN Forum & email list: a extra is subcribe to forums and email list,very important place, enter in the comunity,
thats help you a lot.
OTN comunity forum: https://community.oracle.com/community/developer/english/oracle_database/general_questions
email list: http://www.freelists.org/webpage/oracle-l
4) Read more practise more.
Read all u can get (whitepapers,blogs,forums,books,etc..). Practise all u can… rac,dataguard,backups,etc…
read/practise a forever duty for succeeding as a DBA.