obieone Welcoming people is straight forward. Say how pleased you are to see them, make some general comments about how many people are there, how nice to see new people/ all our regular members, possible comment on weather, little non-contentious matters like that, then morph into the introduction (make sure you speak to the speaker in advance to get a few biographical details etc) state their name, subject they will speak on, their expertise, possibly info about how they acquired it or achievement in this field, then sit down. Opening remarks and intro should be as short as possible. The audience has come to hear the speaker not you.
For the vote of thanks, listen to the talk, make few notes on anything particularly interesting or surprising the speaker said that impressed you. Then thank the speaker for coming, refer to aspects of the talk, ask the audience to show their appreciation in the usual way and as they applaud, sit down and give a sigh of relief, job done.