Hi Fernando,
From your question it is not very clear what you mean by own pipeline.. is it 'stages' by team or is it the visibility of 'lead/ opportunity'
1. If you mean 'stages' you can set unique stages by sales team as mentioned by Sebastien.
CRM > Configuration > Stages, you would need to enable developer mode to view this menu.
2. The default view has filter is 'My pipelines' CRM > Sales > My pipelines so it is likely your users are viewing leads across all teams.
If they navigate through Teams menu they would view pipeline for a specific team as mentioned in Sebastien's answer.
CRM > Sales > Teams click on 'pipeline' button.
If a user removes the team filter on the search bar, they would be able to view opportunities across teams
3. If you mean a users' visibility to a certain team's leads / opportunity only, then you would have to define in 'record rules' for those user groups. Setting > Users & Companies > Groups
Default groups are 'Sales Own documents' and 'Sales All documents' users in both these groups can view opportunities across teams.
Hope this helps!