Linking words (or conjunctions or connectors or discourse markers)

 https://eslforums.com/list-of-conjunctions/

https://www.oxfordinternationalenglish.com/linking-words-and-phrases-in-english/

https://www.grammarly.com/blog/parts-of-speech/conjunctions/

http://academicwriting.wikidot.com/linking-words-and-phrases

https://global-exam.com/blog/en/english-grammar-conjunction-words-in-english-detailed-guide-and-examples/

https://magoosh.com/english-speaking/the-ultimate-english-conjunctions-list/

http://www.english-at-home.com/grammar/linking-words/

http://www.ecenglish.com/learnenglish/lessons/linking-words

http://www.vivquarry.com/wkshts/linkwd.html

http://www.learn-english-today.com/lessons/lesson_contents/exercises/linking-words-ex.htm

http://www.learn-english-today.com/lessons/lesson_contents/exercises/linking-words-ex-answers.htm

http://www.englishexercises.org/makeagame/viewgame.asp?id=2163

http://www.ecenglish.com/learnenglish/lessons/linking-words

https://englishswami.com/linking-words/

Exercises

https://agendaweb.org/grammar/conjunctions-exercises.html

https://agendaweb.org/grammar/conjunctions-connectors-exercises.html

https://agendaweb.org/exercises/grammar/conjunctions-connectors/test-1.htm

http://www.flo-joe.co.uk/cae/students/writing/linking/

https://www.flo-joe.co.uk/cae/students/writing/linking/index.htm

http://www.englishgrammar.org/linking-words-exercise/

https://test-english.com/grammar-points/b2/discourse-markers/

https://www.perfect-english-grammar.com/linking-words-contrast-exercise-1.html

https://www.perfect-english-grammar.com/linking-words-reason-exercise-2.html

http://www.english-practice.at/b2/grammar/connectives/b2-connectives-index.htm

https://www.esl-lounge.com/student/grammar/4g67-linking-words.php

and lots of links to pages of exercises here:

https://www.english-grammar.at/online_exercises/connectives/connectives-index.htm