As a Google Analytics user you are probably quite attached to the default reports in the user interface of Universal Analytics. It can be hard to make sense of the data in the BigQuery export tables.

Let me enable you to replicate the reports you're familiar with. I'll try to keep it basic here.

Device Category Overview report

In the Audience | Mobile | Device Category Overview report you'll find data about acquisition, behaviour and conversion of your users, segmented by device category (desktop, mobile or tablet).

Let's query!

select 
  device.devicecategory,
  count(distinct fullvisitorid) as users,
  count(distinct(case when totals.newvisits = 1 then fullvisitorid else null end)) as new_users,
  count(distinct concat(fullvisitorid, cast(visitstarttime as string))) as sessions,
  count(distinct case when totals.bounces = 1 then concat(fullvisitorid, cast(visitstarttime as string)) else null end ) / count(distinct concat(fullvisitorid, cast(visitstarttime as string))) as bounce_rate,
  sum(totals.pageviews) / count(distinct concat(fullvisitorid, cast(visitstarttime as string))) as pages_per_session,
  ifnull(sum(totals.timeonsite) / count(distinct concat(fullvisitorid, cast(visitstarttime as string))),0) as average_session_duration,
  ifnull(sum(totals.transactions),0) as transactions,
  ifnull(sum(totals.totaltransactionrevenue),0)/1000000 as revenue,
  ifnull(sum(totals.transactions) / count(distinct concat(fullvisitorid, cast(visitstarttime as string))),0) as ecommerce_conversion_rate
from
  `bigquery-public-data.google_analytics_sample.ga_sessions_20160801`
where
  totals.visits = 1
group by
  devicecategory
order by
  users desc