* The InfluxDB HTTP API runs on port `8086` by default.
Therefore, `influx` will connect to port `8086` and `localhost` by default.
If you need to alter these defaults, run `influx --help`.
* The [`-precision` argument](/influxdb/v1.3/tools/shell/#influx-arguments) specifies the format/precision of any returned timestamps.
In the example above, `rfc3339` tells InfluxDB to return timestamps in [RFC3339 format](https://www.ietf.org/rfc/rfc3339.txt) (`YYYY-MM-DDTHH:MM:SS.nnnnnnnnnZ`).
The command line is now ready to take input in the form of the Influx Query Language (a.k.a InfluxQL) statements.
To exit the InfluxQL shell, type `exit` and hit return.
A fresh install of InfluxDB has no databases (apart from the system `_internal`),
so creating one is our first task.
You can create a database with the `CREATE DATABASE <db-name>` InfluxQL statement,
where `<db-name>` is the name of the database you wish to create.
Names of databases can contain any unicode character as long as the string is double-quoted.
Names can also be left unquoted if they contain _only_ ASCII letters,
digits, or underscores and do not begin with a digit.
Throughout this guide, we'll use the database name `mydb`:
```sql
> CREATE DATABASE mydb
>
```
> **Note:** After hitting enter, a new prompt appears and nothing else is displayed.
In the CLI, this means the statement was executed and there were no errors to display.
There will always be an error displayed if something went wrong.
No news is good news!
Now that the `mydb` database is created, we'll use the `SHOW DATABASES` statement
to display all existing databases:
```sql
> SHOW DATABASES
name: databases
---------------
name
_internal
mydb
>
```
> **Note:** The `_internal` database is created and used by InfluxDB to store internal runtime metrics.
Check it out later to get an interesting look at how InfluxDB is performing under the hood.
Unlike `SHOW DATABASES`, most InfluxQL statements must operate against a specific database.
You may explicitly name the database with each query,
but the CLI provides a convenience statement, `USE <db-name>`,
which will automatically set the database for all future requests. For example:
```sql
> USE mydb
Using database mydb
>
```
Now future commands will only be run against the `mydb` database.
## Writing and exploring data
Now that we have a database, InfluxDB is ready to accept queries and writes.
First, a short primer on the datastore.
Data in InfluxDB is organized by "time series",
which contain a measured value, like "cpu_load" or "temperature".
Time series have zero to many `points`, one for each discrete sample of the metric.
Points consist of `time` (a timestamp), a `measurement` ("cpu_load", for example),
at least one key-value `field` (the measured value itself, e.g.
"value=0.64", or "temperature=21.2"), and zero to many key-value `tags` containing any metadata about the value (e.g.
"host=server01", "region=EMEA", "dc=Frankfurt").
Conceptually you can think of a `measurement` as an SQL table,
where the primary index is always time.
`tags` and `fields` are effectively columns in the table.
`tags` are indexed, and `fields` are not.
The difference is that, with InfluxDB, you can have millions of measurements,
you don't have to define schemas up-front, and null values aren't stored.
Points are written to InfluxDB using the Line Protocol, which follows the following format:
